Originally Posted by Stu @ M Developments

Yes, thats exactly it. When we set the EMFPR it is adjusted to get a good balance between cruise and full load fuelling, thats KE's only real limitation. Now at low load and cruise the current pipes may be fine at standard pressure or a little above because we aren't actually trying to send much VOLUME of fuel through the pipes, but when we are flat out and all metering slits are exposed, thus requiring all the volume of fuel we can flow, the pressure we have chosen is not going to be enough due to the flow restrictions presented by the smaller bore pipes.

In a nutshell, at any given pressure we would have supplied FAR more fuel through an injector supply pipe twice the size.