Tip dihedral is more effective than straight, so you could divide the single value for each side so that the total is the same, some middle section dihedral, and the rest at the tip, or raise the middle section some, and the tips some, but the total at the tip being less than it would if the wing were straight-dihedralled.
The ratio of middle to tip... what looks good.
I think this is more art than science.