I must stop looking at this .... perhaps the insert is the wrong way up too. As it is shown in the photo I've posted above, the top of the rack is engaged with the top of the insert level with the "base". So as soon as it was ratcheted up, the rack will enter the hole - so you'll need the big clearance hole I mentioned to allow the rack to pass into the bench.
However, if you turn the insert the other way up there is an inch or so of clear insert beyond the rack. That would mean the insert could pass an inch or so into the bench top before the rack would get to the level of the bench.