I find it kind of wrong that you only able to halfjump once on one height level. I understand that disabling this completely could potentially ruin some maps by making them easier. Some maps, however, are quite long, but flat at the same time, which means If I "waste" my hj in the begining, and sometimes it is needed, some routes will be restricted and thats frustrating. I suggest to remove the "once per height level" rule and make it possible every, lets say, 5-6 normal jumps.
Crouchslide exists too