wat i do is stand on something and with ur other foot stand on a peg. ex.(right leg on left peg, left leg standing on something) then press down on the peg, see if the front and rear moves up and down together. then u get a pretty good idea from there, but not as good as riding the bike though. hope u can understand if not let me know ill help ya.
This is kinda funny... I went through the same thing earlier today. I was checking the suspension on my bike and noticed the same thing you did. I found that squeezing the front brake made a big difference and cause both ends of the bike to move about the same. My KX manual said this, otherwise I probably wouldn't have thought of it... and I don't know how it's valid (you don't pull the front brake in all the time when riding to balance the suspension) but that is what I found.