Thanks for the responses. I checked my fit details from last June, and the saddle was in the same spot as it's been since then, so I'm still not sure why I never noticed it over approximately 1000 miles until this winter.

Having said that, I did the heel check described, and wasn't even touching in my shoes, so I lowered my saddle 5 mm. I still have to get pretty darn straight to get my heel on the pedal, but I noticed an immediate positive change in my ability to maintain a certain gear on the trainer, and an overall lower perceived effort. I also feel after two rides like my post ride soreness is mitigated at least a little bit. I'll have to see how it feels after a few more rides.

Based on this is seems clear to me that my seat position based on my fit was for sure too high, but I still am curious what factors would lead to me noticing it indoors vice out on the road.