I used the FF slider during my 120+ day experiment and on several occasions since.
Some use it temporarily for the day at hand while others (including me) have left it tweaked one way or the other for days at a time. At some point you should return to neutral (0) and check to see how form predictions work in that position.
I don’t claim to know the math behind XATA but it appears the more information you give it the more it adapts to you. YMMV
Reference –
Personalizing Xert’s Training Algorithms by using Freshness Feedback – Xert (baronbiosys.com)