This is really non of my business but here goes. The RYA PY numbers are calculated the same way as the USPN. However, the RYA understand that these numbers don't reflect the true handicaps so Clubs are therefore encouraged to amend the numbers according to their individual requirements. When a Club is happy that the numbers are as fair as reasonably possible they return the new PY numbers to the RYA for information purposes.
At my Club where I have been Sailing Captain for the past three years it wouldn't matter if we used PY, SCHRS or TEXEL the F16 single or double handed, A'Class and F18 would be given the same handicaps. This probably wouldn't work at every Club but all the affected racers here much prefer the fact that first over the water wins. This is what we have become use to and enjoy, boat on boat racing.

Unfortunately, we still have to rely on a handicap rating to score the Dart 18's, F20 and Tornado.

(Pete, if you are racing windward, leeward courses I think giving a little time to the A's is fair. To be on equal terms the finish line should be half way up a beat ;))