I posted this problem over on the REAPER forums. Got a ton of participation there. For any REAPER users, if you haven’t used that forum, they’re amazing. It’s uncanny how knowledgeable and helpful those people are. A really nice complement to IRD.
Anyway, found the problem (yeah. As if I found it! Someone over there found it and explained it to me!).
Turns out that I had some volume automation on the master buss; I had no idea that that volume automation was post-fx. I assumed since the master fader in REAPER is pre-fx, that the fader automation would be also. So, REAPER has another option of pre-fx volume automation, but the default that I chose was indeed post-fx. I.e., it was automating the volume after my YouLean meter and dpmeter3! Hence, the digital peak was higher than my true peak.
Ugh. Embarrassing. Live and learn. I knew I could solve the problem by just lowering the volume and steering way clear of 0.0 dB. Improvising, but not really understanding. Glad I hung in there. Learned something new. Had to share it, in the hopes that I’m not the only one to have missed something like that.
Man, the support and help I get in communities like REAPER’s and HERE are unparalleled in my experience. Very humbling and very cool.
Thank you guys for welcoming me on this journey with y’all. Have never had more fun with my music.