G'day. The old rule of thumb for the main wheel's position is that they should be set up so that about 1/3 or a little more of the wheel is in front of the leading edge of the wing. If it is too far forward, the model will tend to bounce on landing and if it is too far back, it will tend to nose over both on landing and when you are trying to taxi and take off. The safest is to be a bit too far forward.

Cheers

Mike in Oz