[Wayne A. Pflughaupt]

However I still can't see any difference in setting different subwoofer distances on my receiver. I just ran 3 measurements at 7.5', 17.5', and 25' and all three had exactly the same frequency and impulse responses.

In that case I’d just set the correct figure in the receiver and not worry about it. It looks like you are getting the best results with the receiver set to 100 Hz, and the sub set to 80 Hz. The crossovers can introduce their own phase anomalies in the area around the crossover that can affect response as well, as you can see.

I want to solve as many problems as I can passively with room treatment first,

Room treatments (assuming you mean bass traps) reduce low frequency signal decay – i.e., “tighten up” and dampen the sound. This often can somewhat reduce some peaks and valleys in response, but ultimately the equalizer is the best tool for smoothing response.

Regards,
Wayne A. Pflughaupt