The descent rate required to stay on glidepath, regardless of whether it's an ILS or PAPI, is dictated by the groundspeed of the airplane. Remember, the proper glidepath is FIXED. It doesn't change. So the true airspeed (velocity through the airmass) takes you to the groundspeed (velocity across the ground). For most of us that can be too hard to brain slam while we're busy doing an approach so for ease and simplicity, use the approach speed to wag the descent rate. Let's say your approach speed is 130K. Divide 130 by 2. Take the result and add it to the first two digits of your speed. Tack a zero on the end. So... 130/2= 65. 13+65= 78 78 with a zero added to the end is 780. Your APPROXIMATE descent rate is 780 FPM.
One more just for practice. Approach speed= 145K. 145/2= 73. 14+73=87 870 FPM. Remember, this is a wag. And if there's a big headwind having big effects on your ground speed, the rate will be reduced.