I don’t particularly think the front pad is faulty, there’s just more fitting in the whole arrangement than might be expected, and the rear pad is made small in order to shim, as opposed to large in order to machine down. On several occasions I have scrapped the supplied rear pad and machined a new one, larger from scratch as it was less work than building up the supplied item.
It’s the same story for their (Accumounts) k98 turret mounts... without serious rework they simply will not and cannot collinate... pretty surprising they keep churning them out like that but that’s how it is.