The problem, of course, is that your p-values are
way off. :)
Seriously, though, three part
bonuses tend to have an easy, middle, and hard part, of
varying degrees. Assume we have three parts where p=0.8,
0.65, and 0.2. If it is a 3X10, the expected payoff is
16.5. That seems fair. But, if we have a bonus where
the parts are p=0.9, 0.8, and 0.2, they payoff for a
3X10 is 19.0. For a 5-10-15, assuming we successful
gauge which part is which, they payoff is 15.5, if I
did my math correctly, which makes it the appropriate
conversion.
The 5-10-15 is not for when you have a hard-ass and
an easy-ass part, it is for when you have an
easy-easy and a medium-easy part, along with a third part
which doesn't feel insultingly easy if it is worth 15.