I use to have trouble when I changed from field tips to Hunting points with flight right off the bow and would have to raise my nocking point or at least fool with it a bit to get the tail high out, I always had my head horizontal , I started mounting them vertical and the problem went away, I don't know,
but figured it had something to do with wind plane as the bow was released, not sure but solved my problem so Vertical it is for me.
don't think it matters much if flight is good ,the arrow is spinning inflight anyway. Heard and old saying, the Indians mounted there heads vertical for 4 legged critters and horizontal when hunting man, something to do with the rib cage
but as I said they are spinning so that's out the window, but I thought a pretty cute saying.
Pappy