The only way to win at dice is to play 3 strategies at the same time.
Example:
start at 1 satoshi at 10x payout doubling the bet after 5 losses in a row. Reset the bet back to 1 satoshi after a win.
FOR BETTING LOW
At the same time keeping track of any rolls\results of less then 1 and how many bets you have placed. Once you reach 500 rolls without a roll/result being under 1, start betting at 99x payout and double the bet after 48 losses in a row. Reset the bet back to 1 satoshi and 10x payout.
FOR BETTING HIGH
At the same time keeping track of any rolls\results of greater then 99 and how many bets you have placed. Once you reach 500 rolls without a roll/result being over 99, start betting at 99x payout and double the bet after 48 losses in a row. Reset the bet back to 1 satoshi and 10x payout.
repeat
It does not work, I got to earn about 100k sats that way and then, I lost everything... (-75k sats. overall "winnings"). Thanks God those are laughable numbers (it was on multiply game, on freebitco, I did not deposit any money, just with the dust I had got that week).
Besides that, why do you think 20 is a good number?, why not a bigger or a smaller one?