Simply think of the amal valve as a bleed valve, as thats exactly what it is, but its ecu controlled.

To increase boost pressure you need to keep the wastegate closed, so by bleeding air out of the compressor to actuator line stops the gate from opening untill a higher pressure has been reached.
In laymans terms if the actuator has a 10 psi spring, and you want to run 15 psi of boost, you need to bleed 5 psi of boost pressure out of the line.

Now, the amal valve port R is the bleed port, if its to small you cannot bleed enough air out of it, so in some cases where high boost levels are needed, you need to allow more air to bleed off, so incresing the port size is the answer.

i would always reccomend fuelling and boost are carefully monitored by someone who knows what they are doing, as get it wrong and you will lose an engine in an instant.