One calculation we have used for single stage systems is this: You want to start injecting before the torque peak. So on the dyno plot, find the RPM where the TQ is climbing to peak, and look at the HP at that point. Multiply the HP number by 1.5 to get CC/min of an injection amount.

We usually use crank hp numbers for the calculation.

Now, if the car were at 250hp during the ramp, then the jet would be a 375cc as a starting point. Not far from where you are. You can run your numbers to see what it actually is.

One more item to consider, injecting at the TB puts a lot of large droplets in the chamber which can blow out the spark. One thing I would try is moving the jet further away from the manifold, as close to the exit of the IC as possible.