I tried lengthening leg straps until there was nothing more to lengthen - thought NT may have made things too short - but then tried going the other direction ...just to see... Where I ended up was pretty far from where I expected to be, but is probably just about perfect.
For what it's worth, I'm including measurements I ended up with, knowing body types are different so you may settle somewhere much different. A few things not in the pics:
(1) I wear the saddle right at the hips. Other saddles may ride above but this is where NT recommends for the ONYX - or so I'm told - works best for me,
(2) Butt-strap/sling (horizontal strap) doesn't ride directly under the butt, but a little back, and it should be snug, or at least that works for me - I originally had it far too loose,
(3) While sitting in the saddle, approx. 6" space between top of thigh and rigging plate.
Hope this helps.