I've studied these particular displays for some time now and still don't have a definitive answer.The first one(slightly off center) seems better balanced.The tree base appears to be placed in relation to the stand at the same proportions as it is placed in the pot. ,but....it is so "slightly" off center on the stand that if one is aware of "convention",it almost looks like it is there by mistake.If the stand was slightly larger,the tree could be moved even more off center and be a definite statement.
just thinking "outloud"
andy