I've never noticed any issues with getting enough smoke into the meat with my reverse flow. It's not a Lang, but the concept is the same. I did lower the location of the smoke stack, so it ensures all cooking levels are getting kissed with smoke.
Custom 30"X84" competition-style RF trailer smoker
Pecos 20"X60" OS by Old Country BBQ
Char Griller 5050 with side box
Baby Arm BBQ