Personally I don't see any reason why a certain crank length would work better with a certain wheelsize (provided that the bottom bracket height is acceptable, of course!). Crank length has to do with leg length: pure biomechanics, really, and a topic that has been debated to death. If 175s feel good to you, then there's nothing wrong with that. You may just have stumbled upon your best crank length by accident. Maybe you should try putting some 175s on you road and 26" bikes too, to see what it feels like. You may find that you prefer spinning on those bikes as well.