I think it is absurd that they count less than half the rounds you play to assess a handicap. You should count them all , scotch them accordingly and give tournament play extra weight.
I think you are getting nearer, if the system was your best 8 out of 10 then the average we would be nearer the mark, but even that means you could be a 5 handicap and in 2 months suddenly be off 15. We all experience off form times, and I dare say it opens up even more opportunities to cheat although those players wont see it that way. So perhaps there needs to be something that if the rise in hcp over 2 months is more than 2 shots then 16 cards in 20 count. There are lots of faults with the current system. I am 7 handicap and should be 12, but I only have 12 counting cards play a couple of times a year, if I play in Spain it seems hard to register it. If a tee is 11 yards away from a measured position the round is non counting, which to be honest is all a bit crazy. So I think overall if its 20 cards then 16 should count, if you dont have 20 cards in then 4 from 5, 6 from 8, 7 from 9, 8 from 10, 9 from 12, 10 from 13, 11 from 14, 12 from 15, 13 from 16, 14 from 17 and 15 from 18. That is a a lot of shit golf to get to a false handicap and it stop the silly +4 handicappers that are really 2 handicap.
So abandon the 'markers must be within 10 yards of the tee' rule.
16 out of 20. Or the Average of your best 80% cards which will restore a plus 2 handicap being something.
I also think that the increase in prize money you can win has not helped, there are those that search gain from non qualifying competitions because of their format, team or BB. They don't think its cheating.