Are you more upright in a waist harness? I am not, I can adopt the same stance as people that use a seat harness and go equally as quick if not quicker. It is just a matter of getting used to it, get rid of the seat harness altogether you just don't need it. I can achieve a low locked down stance and rig back with a waist harness and feel very comfortable doing it. All about getting used to it.
It is not always neccessary to close the sail right down to the board all depends on the sail and how deep the foot of the sail is. All this seems to do is depower the rig more so perhaps it is not so important in lighter winds