Mark Hamill is 5'9". Not too tall or anything, but definitely not short. Hell, Jango Fett (as played by Temuera Morrison) - who was the model for ALL Stormtroopers back in the clone days, was only 5'7". By those standards, Luke is actually unusually tall for a Stormtrooper.
Also, maybe Leia shouldn't be making such sassy remarks to the people who have a floating torture-robot they can use whenever they feel like it. Or, ya know, a space station that can blow up entire planets.
Those were totally the droids they were looking for.