With a Black book plan , the idea is to make a profit on that horse over its next 5-7 runs, then usually drop it out of ones stable of black Bookers, so as to leave room for another to be added.

Theoretically it should not matter how many there are in the race because we are targeting for one of them to clear their individual slate so they can be deleted from our Stable.
Now this can get expensive if one has not factored this into ones financial resources to fund such an encounter.

The average stat for a horses winning career is approx 16% which works out at approx 1: 6.66 ratio of winning

It is suggested to have no more than 10-20 in ones stable at any one time.
Maybe this helps with scenario.

What I am reading here is that you are trying to profit on a race , rather than treating each horse individually.

It is suggested not to bet if there are 4 or more, of ones horses in the same race.
If we do this & one just happens to win, we have to delete him from the stable & cop the loss on the critter that owes us, but that could be more cost effective than backing all the horses of your stable.

A compromise would be to only bet those that are paying $15+ & take the risk that the shorter priced ones don't get up, because one will kick themselves if a 33/1 shot gets up.

My suggestion if 4 or more in the same race, bet those that are $15+ & cop the loss on any of the other stable horses that owes us, plus delete that horse from the stable, should it get up.

Maybe none will get up in this race & you have saved yourself a Motza.

After all , only one can win the race.

Another thing about following stable horses , is try not to fall in the trap of betting them if they are paying less than $4.50
It has been the undoing of many who have chased this idea because they see a short price & assume he must win, only to be disappointed.
If one does get up under this figure of $4.50 which some will , delete him from the stable cop any small loss, so a replacement can be found.

Don't forget that one has others to feed in the stable, if they don't do their thing over 5-7 runs so value is important.

It might be an idea to work out what percentage of stable horses fail to deliver , that way one will know if the selection process is a viable one.


Cheers.

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Cheers.