Very interesting Harry,have you tried the variation to bet once or twice or thrice the last unique/different lines?
For example,let's the last 3 lines are: second (7/12), fourth (19/24),sixth (31/36) you could bet the last 3 when they are different,in other words you are expecting a repeat from one of these three different.
Optionally you might add up to 2 bets,let's say you have bet the last three different and a fourth different came,now you could bet the last 4 different lines with 2 units on each one of them.
If you win on the first bet,you would win 3 units,if you win on the second bet,you would win 1 unit.
If you lose both of your bets,you may want to make one step further by betting 12 units on each of the last five different lines for a total of 60 units bet.
If you win on the third bet,you would recoup the previous 2 lost bets and add 1 unit to your bankroll.
If you take all 3 steps,you would risk 71 units and you could win 3 (first bet) or 1 unit (second or third bet)
Another way to play this is not to bet 3 consecutive bets but to bet only when 3 different and if you lose,next time with three different you could double from 3 units to 6 units in order to recover the previous trigger.
I have experiment enough with and without money about these variations and I have found that three different lines (18 numbers) are NOT repeating as much as they should,but if you place your trigger to the last 4 different lines you should expect much more wins.
The problem is that by betting 4 lines instead of 3,you are risking 4 in order to win 2,better probability but worst payout.
If you place the trigger on last 3 different lines it's perhaps a bit early,if you place the trigger on the last 5 different it would probably a bit late,thus I strongly believe the trigger should be placed on the last 4 different lines without a repeat.
If we look on this under the law of the third perspective,the average number of repeats within 6 spins on the lines is 2, 2 repeats multiplied by 2 lines of six numbers = 12 numbers (one third) as repeaters and 4 different lines of six numbers = 24 numbers (two thirds)
This is the average,but small deviations might happen from time to time,for example to see 3 repeats and 3 different or 1 repeat and 5 different lines within the last 6 spins.
What do you think Harry?
Which variation do you like more from those I've described?