This is correct, doesn't matter for the accuracy cap though. As an example, nin's raiton is considered magical damage and boosted by foes, but it can still miss from the flank/front if you only reach the rear acc cap.
The 'damage type' has nothing to do with acc cap needed, but as long as something is a 'cast' or 'spell', only rear cap matters. For everything else, you'll need the proper acc cap for whichever direction you're hitting from.
