On the hp4 there is only 2 spots to manually adjust anything. Both are preload and you turn the back with a 13mm wrench, it's backed out completely and it still only has 3/4 inch sag. If I tighten it it's worse, goes to .5 inch then .25 inch, I eventually stopped and returned it to stock setting on the back.
The front is turned all the way out and we still don't have enough sag, it's about 3/4 inch to.
Going to do some research on the web.
2010 Mineral Silver S1KRR
2012 Motosports. S1KRR
2013 HP4 Competition #0373