Risk-averse insurance index numbers?

When I read Blackjack Attack, I thought the section on risk-averse indices was great.

The classic example is 10 vs 10. The expectation-maximizing index for doubling is +4, but that raises your vol so much that your SCORE actually decreases. To maximize your SCORE, you should use +7.

What about insurance? The expectation-maximizing index is +3, but in some cases (e.g. when you have a natural), taking insurance reduces your vol, so the insurance index should be lower. And there are other cases where insurance increases your vol.

I found a technical paper on this once. It wasn't very practical sinc e it required you to memorize a lot of stuff and then take partial insurance in a lot of cases.

Does anyone have a good rule of thumb for insurance? Seems like you could really improve your SCORE if you do this right.

First off, I keep a side cound of aces (with HiLo or Halves) and use this for determining when taking insurance is correct since it has a much better IC (insurance correlation) than simply using HiLo at TC3.

However, if I am right near my "insurance threshhold," I may choose insurance based on what a ploppy might do, or what I feel might reduce variance somewhat. For example, if I have 20 I may insure, if I have 14 I may not. Also I might ask other players at the table if they think the dealer has a BJ and insure or not based on that. I may also take partial insurance or insure only 1 of 2 hands, etc at this time. I do the above in order to attempt to eke out a little cover, but also with reducing variance in mind (don't know for sure if this is mathematically correct, but I figure it couldn't hurt more than a few cents).

NOTE: If the insurance choice is clear/strong, I will ALWAYS choose the Max-EV play!