Here we can see the inner archway/shelf being widened and smoothed.

It is a procedure that takes time and patience. And, you don't just grind the heck out of one port and then move on to the next. You have to do a little on each one and then do the same on the others. That way you gradually get them all the same without going too far on any one individually.

This is not a ten minute job: more like ten hours, to get them all the same.