What works for me is for the PF to have WX-M set at 4000ft-5000ft below crz alt and PM on WX-A. If it doesn't paint at 4000' slice below you, you're quite safe in being able to fly over the stuff.
I'm a fan of this radar compared to the RDR-4B on some of our other birds. But there can be gotchas too, if you have a very intense cell within about 30-45degrees of your track, it tends to mask returns on anything that may be lurking behind it. But i suppose this could be true of any radar seeing as to how it's just the nature of how the RF from the radar is reflected.