In my basement, I have a gas pipe (1" diameter) running between the joists. There is a reason why I have choose this cavity to run a supply line from where. But I am end up using a end boot register which would be perpendicular to the exterior wall. I have seen in my house in the upper living area, builder used 90 degree vent register most of places and, few places the end boot register. In all case, the register vent boots is install parallel to any wall.
Would there be any problem in the air flow, if I run a supply through end vent boot which will be perpendicular to outer wall. The below is the picture I am trying to say. this vent will be just above the exterior door