.....all moved freely ......
I should have emphasized "instant" release.
If the Drums release when letting go of the pedal, you've shown free return "the long way around" to the rear reservoir.
And you've also done the SMC check. Not much more you can do to check the health of your hydraulics.
Not sure the heat would make much difference. The brake fluid becomes thinner and should flow easier. And if the reservoir is not overfilled, there shouldn't be any pressure buildup.
There is one case on the Trike where the PCV is in a situation it doesn't see on the GL (or ST).
On the GL, once the Shut Off Valve in the PCV is closed (when a Honda preset braking pressure is reached), the downstream pressure (pressure to the rear brake) will be equal or lower than the upstream pressure from the SMC. The PCV is limiting (and lowering) the pressure from the SMC to the rear.
On the Trike, there may be a situation where the pressure downstream of the PCV Shut Off (from the pedal) could be greater than on the other side (from the SMC), as unlike the GL you can keep increasing the pressure passed the closed PCV Shut Off Valve by pressing the pedal.
I am not familiar enough with the Shut Off Valve to know for sure if a "reverse" pressure differential across it (Drum Pressure higher than SMC side pressure) could affect it. All I know is that the Shut Off has to move forwards to reopen (against the downstream pressure) and it may not be very happy to do that if this downstream pressure (Brake Pressure) it has to move against is now higher than the front pressure (from the SMC). So there may be some delay before the pressure trapped between the PCV (with Shut Off valve reticent to reopen) and the Drums is released.
On the other hand, only Honda knows at what pressure this limiting Shut Off Valve closes. So no telling how often it is actually activated.
And it should have done the same with the old brakes....unless you've done a much better job this time around with getting all the air out, maybe!
One way to test would be a ride with aggressive braking with the front only (no topping-off the rear with the pedal,,,,while you get an itchy foot!). No pedal, to avoid the reverse pressure differential scenario. And then check if the Drums are still heating up. Not an overly convincing test as the front engages only one piston against the SMC, hence being gentle on the rear anyway.
Another way to test would be, when you get in there to replace the PCV, to make a few runs without the PCV, bypass the PCV altogether. No better way to check if the PCV is in the way or not.
Am not even sure the PCV is of much use on the Trike, as its purpose is to limit the pressure to the rear...while at any time you want, you can override whatever clever things the PCV is trying to do to the rear pressure by applying the pedal.