Thanks for the advice Flash.
Since the Match Play coupon is basically worth half of its face value,
shouldn't the win frequency you use for surrender be 33.3%?
If so, it appears you should surrender 12 thru 17 vs 9, 10 or A,
surrender 14 thru 17 v 8,
surrender 15-16 v 7, and
surrender 6 v 10.