A good question and observation.
All has to do with the dies you wish to use I suppose. But for my personal needs and opinion the less distance you have to cover from the top of the ram to the bottom of the top plate the better the alignment should be between the base punch and the dies.
With my dies I have designed base punches and dies to go with a 1" gap. My dies work different from the Corbin brothers though.
Good shooting and swage on!
BT