@reluctantjumper I really recommend thr team time trial for learning how to draft. Adding extra probably doesn’t fit with your training program but it really helped me. Nothing like Phil’s encouragement to teach you how hard you can push yourself.
With big groups I find the moment you start sliding back you have to do something serious. But once settled in near the back you can gently ease off without dropping out the draft.
Looking at my race I started at 400w but by 15s in was down to 275 and then by 30s was down to 200 ish. But a minute in I lost concentration and eased off too much and needed a big kick up over 350w to avoid losing touch. Popping out the front then sliding back makes it really hard to hold even power. Getting it just right makes a massive difference. In the group on the flat bits I was averaging 230w so really not that different to you.
I definitely overdid it last winter and didn’t rest enough. Just couldn’t raise my power when there was a surge and so kept loosing the draft.
Just focusing on the Tuesday race and TTT is working for me this year as I find them much more fun than training plans. Good luck figuring it out