If you could wire to 2 ohms, you could see if sub movement is stressing the amps too much at .5. You’d see how it plays wired higher, especially comparing db changes over a range, because playing away from tuning can cause way more stress on the amp, which causes the amp to electrically not be able to handle energy from the coil moving more from the woofer unloading, basically. You could try some things like that too. I don’t think any of this is going to be particularly simple or easy to figure out with all of the factors.