You can't see it but the whole plate and the corner and center blocks(the centers are fake-2 halves are scribed to full length railing pieces for strength) rests 1/4" above the aluminum piece.

I haven't figured out how to capture the railing, but I will not puncture that alumimun extrustion. It's carefully and amply overlapped on each corner and two joints in a bed of white silicone. Rain would have to be driven up inside several inches to get inside the building.

I intend to add something-bolted onto the railing perhaps-that will keep the railing from sliding off. The weight alone is sufficient. You have to really force it to move so I don't think wind could get enough purchase on the airy structure to move it. It's seen enough wind up there to blow the caps off the corners(I need to screw those down). It's a different world on top of roofs.