Not sure if anyone has noticed this, but I've noticed at times when facing one unit monsters and doing it as a tactical battle will give me very little XP (sometimes 4-2, or less per unit), but doing the same battle as an auto-resolve seems to net much greater XP.. (Just had one where it netted me +8, and it was just one weak wolf unit..)...
Not sure if this is a bug or not, but I think Tac Battle-Auto-Resolve should give the same XP.