Thanks for the tips.
It seems like I brought it on to myself by attacking the homeworld with the CPA post first
, upping the AIP to 400 in the process.
I hadn't unlocked any Mk II turrets either because I needed the research to boost my numbers (had been given only swarmer type ships by ARS's) so my defences were on the weak side.
I usually wait untill a medium group of CPA attack's one of my planets and the destroy them one group at a time but this time that was quit impossible due to the large numbers, an exo strike and the number of high mark tractor platforms pulling my fleet apart.
Does the core CPA affect normal CPA's and vice versa ?
Just after the core CPA hit I got the normal CPA warning telling me there were another 3000 ships waiting in line to crush me so I wondered if the amount would be affected by the recent AI losses during the CPA and my thread hunting afterwards.
I didn't wait untill the CPA hit but broke through though and killed the second homeworld so I wouldn't know.
The black widow golems and the spire ion ships saved the day in the end.
My next game will be my first Fallen spire game so I image I'll be able to test all the defence layouts propsed here.