For some reason I find that structured workouts produce a much higher RPE for a given XSS than unstructured rides… Example 100XSS/hr structured workout is very painful but the same xss/hr for a nice fulgaz ride feels much easier.
Just an observation but, any idea why that is?
And am I getting the same training benefits (focus seems to be similar)
Assuming the XSS & Focus are comparable, then yes, you’re getting the same benefits from these activities. In fact, this is what makes Xert such a valuable training tool - your unstructured rides can be accurately analyzed and considered ‘training’ 
Could you possible share the MPA charts for a structured ride that felt hard and an unstructured Fulgaz ride that felt easier?
What was the Focus (& specificity) of each? What about difficulty rating?
Easier - 3.5 Difficulty - GC Specialist - Mixed
One example
Bulls on Parade is certainly not an ‘easy’ workout! Notice how quickly the difficulty in response to your MPA dropping.
The immediate difference I see between these is that the workout forces you to ride at a moderate intensity while MPA is lowered… in the other activity, your harder effort was followed by easy pedaling which allowed your MPA to recover before you continued on. In fact, that’s drop in MPA is entirely the point of the workout! Endurance under fatigue (with lowered MPA) is how it’s possible to accumulate strain at relatively high rates whilst still being below TP.
Ok but bottom line, Bulls on Parade has this profile:
Duration: 1:12:00
Focus: Climber - 10:13
XSS: 126
Difficulty:3.5
Nearly the same as my free ride, actually free ride had XSS of 140 in same time. Will I get the same training benefit from both?
(Btw, at the time I had attempted both of these I was two full stars)
XSS/Difficulty Rating are very important, but not the only components influencing RPE. The other factors are such as temperature, humidity, altitude, cooling and ventilation, hydration and nutrition, mental stress etc. RPE can be significantly different for exactly the same effort, if executed in different conditions.
Maybe the difference between ERG and SLOPE is a factor as well. ERG feels different, a bit like a fixie outside. For me it is kind of ‘Zen’ as it takes some of the decision making and maybe some need for motivation out of it. But I tend to avoid big/long red blocks with no ‘escape’ when deciding which workout to do.
Or maybe it is the difference between riders with more HIE and riders with higher TP as well. The free ride looks more HIE, less TP to me, kinda what my body prefers as well, spikier? To test this maybe try another workout that ‘looks’ more like what you do naturally.
Something like Raining Blood?
https://www.xertonline.com/workout/qx7ojkbcgfkxewtu/view
Shorter focus though, so maybe not quite the right one. But it is tough but fun. I should not even be able to do it, maybe because I keep my signature a bit low to make the fun stuff doable instead of only doing 1 diamond boring endurance workouts 
The last piece to consider here is specificity… What was the specificity of your free ride? I’m guessing it’s quite low (either Polar or Mixed).
Definitely True.
Was mixed focus
As to why the unstructured ride felt and was easier consider the flipside to MPA drawdown is MPA recovery during RIBs. As Scott mentions, “easy pedaling”.
Notice how many times and how often you had RIBs in blue on the “easier” ride and virtually no blue on the failed workout. While MPA is restored while in green (SS territory) it’s slower and very different RPE. You’ve left the comfort zone.
Had the structured workout included similar blue recovery points you might have been able to complete it. The alternative would be to dial down intensity or switch to Slope mode and force some blue into the mix. Sometimes a short break where there is none is all you need to keep going. Other times by halfway in you realize “nope, this ain’t happening today”. 
If ending stats are similar focus, difficulty, and XSS you accomplished the intended goal. Same as when you free ride to focus outdoors versus selecting a workout to ride indoors. Different chart profiles, but similar training benefit.
When at two stars, selecting a 3.5 diamond workout is sure to be challenging and prone to failure. You can view the workout in Workout Designer with your signature applied before deciding. I am cognizant of the blue/green mix and frequency before making selections. IOW I’ll wimp out and take the easier route when I can. 
Consider circling back and try the Bulls workout again when you’ve reached at 3.5 stars. It will be tough, but completion is likely.
Thank you for the explanation, if it has the same benefits I’d much rather do a free ride that is above my pay grade and more enjoyable anyway 
Practically speaking, it’s Sunday and I am behind in my training for the week, I can either do a structured workout or something unstructured and achieve 150% of the suggested workout xss in the same time frame. And like you noted, if I had chosen a 3.5 diamond workout I’d fail it, but yet achieved the same difficulty level on the unstructured workout.
I’ve had tons of “fun” in summer looking at a target for Difficulty, Focus, and XSS, and then just jumping into a ride without any forethought about what the intervals would look like. @ManofSteele brought up Specificity, and I that’s the real kicker. For me, I could shoot for a high Diff and XSS, but getting a pure, as opposed to mixed or polar, Specificity is really hard.
But does it make a difference?
Probably not much. I think you’re getting down to very good vs perfect, at that point.
This slightly changes the topic of this thread, but yes, it does somewhat matter.
If you’re riding mostly at endurance pace and toss in a few short, hard efforts (let’s say 5:00 power), the Focus duration will decrease (from 3:00:00 down towards 5:00 focus). But the specificity will be very low, since very little XSS was actually achieved at that power.
Compare that to an activity where you either soft pedal (<100 W) or ride exactly at your 5:00 power… the specificity would be PURE, since most/all of the XSS achieved would actually be accumulated at/near your 5:00 power. Hope that makes sense.
