Kelly Size on an In-Between Bet

You hold a 2 and a 10 dealt from a fresh 52-card deck. A third card comes off the remaining 50. You win an amount equal to your stake if the third card's rank is strictly between 2 and 10, and you lose your stake otherwise. Ties lose, and the payout is even money.

ranks_between = [3, 4, 5, 6, 7, 8, 9]
cards_left    = 50                      # 52 minus the 2 and the 10 in your hand
winners       = 4 * len(ranks_between)  # four suits per rank
p             = winners / cards_left

You will meet this hand thousands of times and you want to maximise the long-run growth rate of your bankroll, not the profit of one hand. What fraction of your bankroll should you stake?

Answer format: round to 2 decimal places.