JVH, just something to try - when the main port duration is 190* to 192* with the pipe length adjusted to suit, I have found more overall power
due to a naturally very wide band of superposition prior to EPO.
This may also allow more timing split with the Aux ports, so their differing ( longer ) duct length has less effect on the wave amplitude generated by the main port into the diffuser.
But this may not show up as a huge difference in EngMod as there is no mechanism in the code to define the Aux ports duct length, only an assumption on my part - dangerous.