When researching this, I also spoke to an outboard motor mechanic, who was a hot-rodder and a racer. He explained, its simply a matter of balance; getting more fuel in, in the right proportion. That's why a bigger jet (more fuel) is combined with a bigger inlet (more air).
A further increase to 30 would have been possible, but necessitated a bigger exhaust outlet which would have involved removing the power head, so I didn't bother. Again, a matter of balance: more fuel/air in, needs a bigger hole to get the exhaust out.