At work we have 1U servers mounted on a two post rack. Every time I have to do any kind of work on the rack I basically have to do yoga to get at the back of the rack.
As nice as it is to get a full body workout every time something needs to be added to or removed from the rack, I would strongly suggest you avoid racks that can't be accessed from the back like the plague.
On the upside I have discovered unique ways to string together curse words while fumbling behind the rack.
Science is what happens when preconception meets verification.