Actually the PAPI is set for the designated GS ie 3.0/3.25/3.5 to the touchdown point. Just follow the correct combo of red and white for your acft.
So regardless of the runway gradient or slope, you should follow the PAPI and touchdown at the chosen spot in the windshield.
This may give you a high rate of closure with the ground landing up slope so an early flare may be called for - conversely landing down slope will need a little less flare. In PNG we were routinely landing without aids at runways with up to 13% slope - and on one earthquake relief task for the UN in Irian Jaya, one section of one high DA mountain strip was 25% slope - made for some short landing rolls
And lots of power to make the parking bay for the three point turn required to depart.