No. The club give you 80% of the 1/19th of the season ticket cost and only if they can resell it on for the match day price, which is obviously higher than season ticket average game cost. For category A games, it's near 100% profit increase for the club.
I've no issue with the club making an increased profit by reselling at the higher match day price, but I think the ST holder should get the full value of the ticket (ST cost/19), even if the refund was limited to say 3 matches per season before the 20% charge was triggered. This would prevent people buying STs just for a few games, knowing they'd get a full refund for all the other games.