Sennadog,
My instructor taught me thus.
When established on final, trim for your approach speed, then kill the power, trim and maintain airspeed. Forget the PAPI'S look at the threshold. Try to keep the position of the threshold constant in the winscreen, MAINTAINING airspeed. If the threshold starts dissapearing under the nose, you are too high, if the threshold starts climbing up the windscreen, add a little power, but only until it stays in position. You should then be able to fly down the glide slope. Worked for me anyway! Good luck.
Iain.