Dharan - 42.9% more is the multiplier of the bonus.
If the elf has 50% bonus, the Dwarf would need 1.5*1.429 = 2.1435, or 114.35% science bonus.
Dw: 3 * 2.1435 *.7 = 4.50135 mod TPA
Elf: 3 * 1.5 = 4.5 mod TPA
My edit was because simply having 20% more BPA wouldn't give you a 20% larger bonus, you would need 400% more BPA for a 20% bonus.