Yes an overlap would be an issue as it would allow the snake to push and open the tub.
Chris is making new racks, where V18 and V35s and even V15 are interchangeable and therefore built with the little extra length accommodate both tubs, the old ones are meant for V18 alone I am sure.
Some of his new rackd (which I have seen 3 weeks ago) have shelves that are all equal in height capable to accommodate either 3 v15 or 2 v18 or 1 v35s tubs.