I've only studied photos as well, so my knowledge is appropriately limited. Most of the photos I've studied are of guns where the back of the lock is rounded, but ones with the tail are not uncommon. Sometimes I leave it on, sometimes I take it off. Just depends. My personal gun is a Southern Mountain rifle, with the Chambers Late Ketland; and I left the tail on that one.
Chambers' Late Ketland lock plate has plenty of metal behind the sear and sear spring; so you can round it and still have good inletting contact at the rear of the plate.