Positioning, and a problem

I started playing with the position of the elements, and I notice a problem. Since I decided to go straight across the interior of the module instead of at an angle so I wouldn't have to cross the heater core trough, I had less surface area than the original plan. Take a look in the top left corner, and you'll see where I traced in red the outline of the plastic flap shown in the round highlight at the lower left of the photo. The flap can be cut away, but notice the step in my red outline. This is the corner of the foam-covered vent selection flap. That's pretty close, and can't be moved.