"The Blackjack Life" by Nathaniel Tilton

[Norm]

Indices can vary depending on how many other indices you use. But, the effect on overall results is minor.

[Three]

Only one index should produce the highest risk-adjusted return.

Read BJA3 pages 370-378. One of the terms in the equation for solving RA indices is the size of the wager expressed as a fraction of the Kelly-equivalent BR. The equations being solved simultaneously reduce to when the latter term equals 2 times the delta EV divided by the delta variance between the two decisions. So what the RA index actually is depends on the size of your bet expressed as the fraction of the Kelly-equivalent BR. So the use of the RA index should be based on your bet size. If you have a small bet out use the EV maximizing index. If your bet is big enough you use the risk averse index. How big is big enough is determined by the equation I spoke of above:

Critical bet size expressed as a fraction of the Kelly-equivalent BR = 2*(E1-E2)/(V1-V2)

Keeping the term RA pure, you are right there should only be one RA index. But the when to use the EV maximizing index or the RA index will depend on your bet size and BR. With that said different RA indices can exist if different criterion are used to calculate the RA index. Like Norm mentioned number of indices will affect it. Your call on how RA you want to be will affect it. Adding a side count that makes the weak decision stronger will affect it. etc