I just had a thought UB, couldn't you have the 'Field' race be any of the 4 legs that you want? I understand you prefer it to be the last leg so you can hedge with the approximates but surely it also makes sense to identify the roughest leg of the quaddie and make that your 'field' leg.

So you could do the last strategy on the first leg, your horse wins so quaddie remains alive, field 2nd leg so no laying required, then follow the lay strategy 3rd leg, and lets say it wins again you could then just lay your last selection appropriately in the last yeh?