The gap is decoration. Go find the CAD on the home page and look at the measures for magwell depth, then measure yours......
Wait till you get a lower that the magwell is farther down than drawing, the block will not set into the well deep enuogh to latch the mag catch. I had to swipe the bottom of my magwell with a file to allow the block to latch in the mag release. I have a friend with a SENDRA RR M16, he chose to mill material off the Hy-Tech.
The block is probably cut more to spec via AR blueprints than any lower out there. Using the Mag catch as an X/Y axis "0", all points from there should be correct, that is why the block works typicaly 100%, as the ramp is correct height/ejector correct height.