OK you can do this by hand if necessary
(1)First you find the relative frequencies of each type of 20
(2)Then you find the payouts for each type and multiply by the relative frequencys.
(3)You arrive at the average payout for having a 20.
(4)You then determine the probability of having any 20 that gives you positive expected value.
(5)You then determine the density of tens that will give you this probability in step (5).
(6)You determine the most probable full pack composition for a true count of +1 as the basis for further calculations. The rest will initially assume balanced counts:
_(a) Take the size of the full pack, in decks and multiply by 1/2 the number of low card or high card points.
_(b) Divide by the number of high cards (counting each tens rank as a seperate card type) per suit. this is your number of high cards you add. Example for six decks you add .6 tens, jacks, queens, kings and aces if you are seeking a +1 TC, for 6 decks and hi-lo.
_(c) Divide by the number of low cards for the similar number of each low card to subtract.
_(d) A most probable TC=+1, hi-lo 6 deck pack is: 12.4 2s to 6s, 13, 7 to 9s, 98.4 tens, and 24.6 aces
(7) From the this pack you estimate how high a TC is needed to have a tens density that matches the result of step (5). A TC=+1 shifted the tens density from (4/13) to (98.4/312).
The alternative is to follow the same steps you might use to find an insurance index algebraicly, where you use a point version of the ten count and (tens-9 all others +4), and find the index that realtes to the result of step (5) and then use Snyder's Algebraic Approximation paper to find the hi-lo index.
No kidding that payout schedules varry greatly. I skipped where you already had an estimate going for how high a tens density would lead to positive ev also--got to save something for the Greenchippers, I would like to join, except for the ex-es, to do;-)! My Blackjack Therapy ms. can show you how to find the balanced equivalents of unbalanced counts too---shameless plug for something I gave out for free (I know dumb).