I swapped out the PSU for my RasPi which has FA Blue 1090MHz and RadarBox Red 978MHz dongles. Didn’t have any particular performance reason but it had been something I’d wanted to do for a while. I replaced a ‘wall wart’ plugin USB device as supplied with many RasPi kits with an 5V 8A PSU.
Very surprised to see an almost doubling of the message rate. The dongles are on short 6in USB cables but it would seem to indicate they mush have been having either performance or communication problems with the smaller PSU.
Posting this so others can see the impact of the better PSU.