your plane should balance out at the same location.

Something that you also want to check, is that when your airplane is level in comparison to the wings, not the gear, that your cg is still aft of the axels. If it isnt, it'll nose over on takeoff every time.

Oh yeah, and that affects where the main gear goes, not the CG.

That's it! try sticking your gear on with a bit of tape, or a drop of glue to check it before you put it in place permanently.

One thing not mentioned above; if you get the main gear too far forward of the CG, landing will become difficult. The plane will tend to bounce back into the air very easily. As a general rule, having the axels of the gear right under the leading edge of the wings when the airplane is level is about right.