Hi Top Rank ,
You a correct in that respect, it is done this way to give it a more realistic actual chance of winning , there is no point trying for value betting if ones book value is say 150% over 5 horses ,it has to be closer to say 90% or less if possible , so by adding one point , it evens out the spread , especially on the shorter priced horses.
e.g. 2/1=33% as opposed to 1/1=50%. Book value diff =17% this difference is the amount you dont have to recover if it looses.

Cheers.

__________________
Cheers.