Belmont I believe you have a good suggestion on a permanent rule change. If a horse or part of an entry is scratch from wagering and does run or other part of the entry runs then the race becomes an all for horizontal wagers.

I believe but not positive that if one part of an entry is scratch after the first race of an horizontal wager you stay with the other horse in your horizontal. Although not exactly the same situations this is fair to all , treating it the same way as a change in surface.