I HAVE ACTUAL MEASUREMENTS. These are with my calibrated SDR settings. Iris set to manual 0. I'm not accounting for screen gain in any of these.
21.83 ftL low lamp
32.79 ftL high lamp
26.01 ftL low lamp
38.92 ftL high lamp
So there is a 19% bump in ftL! Looks like the calculator was indeed off! Though the JVC's zooming does appear to knock out some of the advantage.
What's really interesting is that I measured my normal 16:9 screen (100") and came out with ~24 ftL in its calibrated SDR setting with the iris set to -5. ChadB measured it at 20 last year, but he was taking it off the screen which had a measured gain of about 0.8, which means the actual measurement today is around 20 as well.
My XY screen seems to have higher gain than my 16:9 screen, though I'm just eyeballing it. Based on this the zoom method appears to provide adequate brightness. Assuming the measurements are accurate of course.
JVC RS-520, Elite Screens 16x9 100", XY Screen 2.4:1 115"
Klipsch RP-8000F, RP-450C, 2xRP-240S, 2xRP-402S, 2xSVS PB-1000
Denon AVR-X3200W/HDFury Linker/MiniDSP 2x4 HD
Panasonic UB820/PC/PS3/PS4 Pro/Switch/WiiU/Xbox One X/Original Xbox
Logitech Harmony Hub