If you want to get technical that percentage of messages has an amplitude of 0.7 or greater.
A large percentage is an indicator that probably some messages have an amplitude to large to be detected it’s unknown though how large that percentage is.
Even when i set my gain so that i get 10% Messages > -3dBFS i don’t see a drop in Message numbers. But i can guess that then i’m probably losing a few percent of messages or something. Not that you can really detect that as you may decode some more weaker messages and 1% variation is really small to see compared to traffic and weather changes.
Only @retman1222 with his splitter can only really make any measurements on how many messages he loses. And even he would need to do each measurement in reverse with the dongles switched or something because the dongles are different as well.