You will never hit the x1000 multiplier on medium risk because it simply isn't on the board at that difficulty. You have to manually change the settings to "High" risk and select 16 rows to unlock the outer edges where the big wins are located. I found a useful link that explains how the probability distribution changes based on the row count. Just remember that at a Plinko Casino, high risk means long dry streaks, so manage your balance carefully.