I agree with Shaggy that you ought to forget about PAPIs for visual approaches in light aeroplanes. As your crosswind trip may have indicated, the plan is to learn to land on any runway, not just a particular runway. At many GA fields there are no PAPIs and the only thing you get in the undershoot is a bunch of nimbys throwing rocks at you, and attempts to use these as approach aids meet with mixed results
May I tentatively suggest that your instructors have got their airline hats on too tightly if they have been encouraging you to look at lights on sticks. The squished bug on screen (aka spot that does not move) method is well described in Langewische's commendable tome "Stick and Rudder". I'm just fed up with all the fuel I've burned flying around trying to get the bug in just the right place.