I’ve found that 80-90% of LTP is fairly easy (nose-breathing effort) and almost always ends up around 60XSS/hr pace. It’s possible to use difficulty score to pace things… keep difficulty score below 60-70.
I think you could also use the workout designer to find out what power will result in a certain amount of XSS/h by using the XSSR power measure. Above 100 XSS/h it becomes curvylinear as you accumulate more XSS for less power under fatigue, XSSR is a constant effort not a constant power. 100 XSS/h is as far as I understand it your TP. Below 100 XSS/h it is constant since Xert assumes all endurance efforts to be constant with no fatigue (but that shortcoming has been talked to death already).
I really love when well above TP the curving downward XSSR blocks of a smart workout lead to rectangular heart rate blocks really suggesting a constant effort in a measurable way. When the heart rate stays more or less constant for the block while the power declines. I get that when my signature is correct and I feel fine. That’s the magic of Xert 
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Here’s how I’d use this guidance:
Difficulty rating is 2 star, or 50. During the ride, make sure you can see Difficulty on your head unit and don’t let it go too much above 50. If you’re pushing any time you’re close to 50, ease off. If the high water mark for Difficulty is 25, you could have gone a bit harder, but if you still hit 122 XSS, fine. If we get to 75 Difficulty (3 stars or Difficult), you definitely went too hard.
The Focus is long, which means lower intensity (Endurance). On your head unit, Focus should be 60 minutes plus. If your head unit allows, you should aim to keep Focus at 2 hours and 10, or close enough to it. On Garmins, the Focus number goes away once it goes over 60 minutes, so ideally you don’t want to see a Focus number at all on Garmin.
The target for any “efforts” should be around 234w, but the primary objectives here are getting to 122 XSS and getting the overall Difficulty of the ride right. Looking at Difficulty and Focus, this is pretty easy to execute. If Focus or Difficulty changed, the strategy wouldn’t change.