1.5% of the total bankroll:
6438 and some change * 0.015 = 96.58
(50 * 96.58 * 1.02) (50 * 96.58) = 96.58
If in such a scenario the game multiplier were to reach 1.03x, bustabit would be risking not 1.5% but 2.25% of the total bankroll.
max bet has increased to 97.09 now but the principle remains the same
as you can see in the screenshot below that the max bet right now at bustabit is 97.09 so if bet that amount you need to reach 1.66x to make the game instant stop because it reaches the max profit