It also makes sense because he has to shoot from both sides of ladders too.
Doofenshmirtz: This is a little bit awkward but have you seen my escape jet keys? (Perry nods) What, you have? Well that's great! So where are they? (Perry looks away) You won't tell me? Is this because you don't speak or are you just being a jerk? ~Phineas and Ferb, "One Good Scare Ought to Do It!" (2008)