That hydraulic crimper scales up hand crimpers for insulated terminals, the proportions don't seem to compare.
If I had to guess, that dent reduces interior 'volume' like a hex crimp.
But; can't visualize how indent equals same all round compression, especially the two pocket areas next to it. Pressing round into a crescent isn't logical.
Regarding the seal, have gotten unbelievably good results with adhesive lined shrink tube.