CAUTION: Information overload approaching 
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Xert’s Power Curve is not built strictly on MMP data points.
See: Is PP a theoretical number? - General - Xert Community Forum
There are three Power Duration curves shown for every activity. MMP and Signature curves for the activity plus Current Signature.
See results of my initial 120+ day indoor experiment on Xert. YMMV 
Pre-Base to TED; 120+ days; 100% recommended workouts completed at 100% difficulty - General - Xert Community Forum
The dip is due to periodization being applied in respect to your current TL. It is more pronounced the further the target date is away. IOW there is no point jumpstarting a progression if the goal date is many months away. You can start with a taper. 
If desired you can adjust the Periodization Level and recast the plan to view the changes.
When your signature is dialed in, I think you’ll find MPA draw down is accurate across the range of efforts above TP.
You should be able to complete most workouts at 100% intensity in ERG control mode whenever your Status Stars count equals Diamond Difficulty count. That’s not to say at 3 Status Stars TL you can’t tackle a 4-diamond workout but it will be harder depending on Focus Power and Specificity.
Note: Exporting SMART workouts to Zwift may lose some functionality present with the EBC player. Some intervals can be harder or easier than intended when performed on Zwift. This is only an issue for HIT workouts that contain Target %MPA intervals.
It is recommended to validate your signature before running a forecast (or recast after a BT) –
See this “fitness test” workout post: From old trainer to smart trainer. Set FTP - Training - Xert Community Forum
Also: Breaking Through the Xert Way! – Xert
A forecast plan is not limited to predicted improvements but an estimate based on recent TL and calculated changes to TL (low/high/peak) and Signature values between now and target date.
Don’t hesitate to push the limits of the prediction by running a forecast with Achievability warnings into yellow like you have done or even red. You can always review the what-if result before deciding to save.
Regardless of what the forecast indicates, you can improve upon the prediction during the plan and recast as @tommying mentions.
Indeed, you can adjust and tweak a forecast if required throughout the duration of the plan. But the ability to take any detours narrows as you approach your target date.
HR is useful for analyzing activities without power; preferably with cadence. See HRDM.
For a deep dive on Xert’s approach see this blog post –
Entering the Performance and Training Multi-Dimensional Universe – Xert