I have 2 mountain bikes. I ride my old Gary Fisher Montare on my trainer and my Sugar 3+ full suspension on the trails.

The problem is that the frames are very different between the bikes. I have a longer stem in my Montare but a regular stem in my Sugar and different saddles in both.

Lately, I have been riding both bikes and experiencing knee pain. I noticed that my saddle placement (fore/aft) is pretty different.

Should I have the same saddle placement (fore/aft) in both bikes? Regardless of the saddle type?