What Jon said, plus... My guess is going to be that, while sprinting, most front end flex is coming from the bars & stem. Carbon steerer might be playing into that equation since (iirc) stems are not torqued down as hard as you can on an AL steerer. One thing you can do with the current setup that may help is to 1. make sure theres carbon paste on any carbon parts, 2. fasteners have blue loctite or similar to prevent loosening, and 3. all fasteners are torqued to max spec.
I had issues with my headset coming loose (just a tiny bit!) on my compact, and eventually solved it by epoxying in the expansion plug and then going through the list above. I only weigh 160 but I was loosening up parts until I did this, and I'm 99% sure it was from aggressive sprinting, esp on hills. It really helped "solidify" the front end feel.
2010 Ibis Mojo SL
2005 Moots Compact