The thing to remember is that although stacking five racks high means the weight of four racks is on the bottom rack, the bottom rack is spreading that weight across 100 chips. In theory, each chip is really only bearing the weight of four other chips (plus 1/100 the weight of four racks.)
The catch is that the chips are not 100% uniform in size... so a chip that is slightly wider than 39mm is going to bear a lot more weight than its neighbors. Perhaps 8 or 16 chips of weight - or more if it's very wide of if there's something else in the rack under the chip.
So the oversized chips will bear more weight and be crushed down to size. Win.