Looking at it from an automotive point of view (ie not A7 specific) I'd say the radius at the bottom can do no harm - helps to reduce the possibility of failure. The fact the slot is longer should make no difference, as it's at the base of the collets, whilst they seat at the top. There has to be some clearance, and unless it was manifestly excessive, can't see how that would deleteriously affect things. Just my 2 cent's worth...