Why is there more than 1 solution that requires 20 moves in rubic cube solving?

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Imagine a group generated by this 3 elements

1, x, y

Say there is no relationship whatsoever between x and y and say both are cyclic of order 2. We know that the group must have at most 4 elements right?

I mean, 1, x, y, xy.

Am I correct here? So there is only 1 element "farthest" from identity, namely, xy.

I must be a bit wrong here because yx may not be an inverse of xy, but I think I am on to something.

So it seems that the fartheest element on a finite group should only be 1 at most.

Am I wrong?

Actually, if a group has generators with limited cycles, is there a way to measure the number of all distinct elements in the group? Why is it so difficult to proof that the God's number for rubic is 20?

I mean all rubic position, assuming that the center never moves, can be generated with 6 elements with 4 cycle each right. So is there a formula that can compute the number of positions that can be solved in 1, 2, 3, 4, 5, 6, ... steps?