I don't know. Its my first build. How high is too high?
The buffer retainer height is set by how far you screw in the stock buffer tube. The tubes generally have a little notch to fit around the buffer retainer. The notch limits the adjustment to full turns of the buffer tube.
I can't tell what kind of tube that is, but some pistol tubes space off the fixed ring on the tube... I'd hope screwed in "all the way" is right for those. Basically, you want the tube to keep the buffer retainer pin down to catch the buffer only.
Actually- now that I think about it, I might be totally wrong- the BCG is supposed to have a notch on the bottom to ride over the buffer retainer.
Sorry- back to square one.