Cheers, my friend
Ha! Correct about the comb spine. Like so many other handbooks intended to be read and reread (Humman's fantastic ID set, eg), the flat splay was indeed intentional. A paperback that thick would never hold up to such reuse and a hardcover would still not lay the same and be too expensive for many folks. At least for a first release/pressing.
As far as location for fragging, there are fewer "rules" for scleractinians. Affect on water flow (in and around the colony) and aesthetics are bigger influences than any health concerns. If you like most aquarists are using static lighting (non-moving, as in tracks for lamps or natural sunlight), then I would look for a convenient lower or interior branch that will ultimately be starved of light in time.
If you are fairly new to it all, though, just make it easy on yourself and prune an asymetrical outside branch and make the break somewhere back near the "node"(crook/fork) of a branch- like pruning a plant... if only for aesthetics again.
The frag could literally be a 1/4" and still survive (as many will attest), but it would be safer to take a fragment closer to 3" long to improve chances of survival.
Do take some pics before and after the fragging and post them if you can
Kind regards,
Anthony