If you have a single-speed or an internally geared hub (i.e. nothing else taking up chain slack) the correct position is when your chain is at the right tension.

If you have a rear deraileur, the correct position is the same position as when you adjusted the deraileur; which is why the world switched to vertical dropouts.

Where you moved your wheel to probably just closed up the deraileur adjustment to closer-to-optimal; you could probably get the same result with the wheel all the way back by twiddling adjustment screws, which I might do since "all the way back" is at least a repeatable position. The adjustment screw some have lets them pick a different repeatable position; exactly where the wheel goes has some effect on handling, but this is probably more subtle than you care about if you ride that bike