Exponential XP costs mean catch-up is almost always 1 Level per session.
Of course experience awards aren't a "punishment", they're a representation of a character learning by *actually experiencing* things. So if a character isn't present, they don't get any. Someone who contributes less to the game, gets less from the game.
It's one of the most deranged things I've heard. Won't play if there's a Level gap?!