Carlson's advice is a bit dated...
Ian... Andersen? ;-)
Under good conditions, you CAN make money with a 1:2 spread at SD. Carlson's book was written at a time when a heads up single-deck player could expect 7 rounds (RO8). A heads up AOII counter playing a H17, DA2 game with 7 rounds to 1 spot could, by betting $27.05 at +3 and below, and $54.10 at +4 & up, make $41.81/hr with his $10K BR, with a RoR of 0.9%.
However, more typical these days is 5 rounds to 1 spot, where our intrepid AOII heads up player spreading 1:2 would make only $12.32/hr with a $10K BR and a 1% RoR by betting $14.55 at TC up to +1, and $29.10 at TC of +2 & up.
That's why these days we need to play with a somewhat larger spread. For example, in the RO6 game, if the player spreads 1:4, he can make $33.55/hr by betting $16.90 at +3 & down, $33.80 at +4, $50.70 at +5, and $67.60 at +6 & up (with 0.9% RoR).
With the right act, even larger spreads can be achieved. Spreading 1:10 ($12.10 to $121.00) will achieve a win rate of $57.93/hr with a RoR of 0.9%. You'll have to wait for at least a +12 TC to place your max bet, but under these conditions that'll happen 1.58% of the time.
Hope this helps!
Dog Hand