Hi, it's Jenna Robbins.
It goes the other way because you're halving the rates. When you half the general rate, it's a greater rate reduction than if you half the small business rate.
As my colleague says, it's preferential to the taxpayer. It gives the best result. It's like an ordering. You order your income first into the general rate and then you apply the reduced small business rate for manufacturers, and then on to your ordinary income, your general rate and then your small business rate.