Clint, nice growth!
My only "grit" was from older mixed potting soil with some light fertilized commercial offering. I wanted "plain" Fafard Commercial Mix potting soil that I'm used to. Those 3 Waves were slow but when they took off it was gangbusters. Annuals, no complaints. The ground-grown plants are doing exactly what I'd expect. Lots of years of experience with begonias and impatiens . I had no interest in Wave petunias until you couldn't get away from them. They're nice. I'd rather pot standard petunias considering what I'm seeing?
Just my speculation but this pot probably isn't getting enough sun? Growth and blooms are still respectable and I know our temps are hotter. I can fix the pot with new plants but I don't want to.
Loss and replanting isn't the end. I might re-up with simple scissors? I'll add a pic.