Dreaded P0A80 Code - Car Running / Charging Good.

Mixing coolant is not good. You run the risk of it jelling up, and not flowing.
But it's done.
If you fill it slowly, and a little at a time, you won't have to worry about air pockets because the coolant
will push it out.
If the coolant temperature is within specs, while driving, it's likely working correctly.

 

Yes there is a good flow entering from the top reservoir hose once the thermostat opens. Flow before the thermostat opens uses the thermostat bypass inlet. Even after the thermostat opens a majority of the flow returns via the big radiator hose.

Regardless there is a decent flow through the reservoir after the thermostat opens.

Due to the somewhat opaque plastic of the reservoir, I place a small led flashlight directly on the top of the reservoir to light up the inside, making the flow clearer.

A portion of the gen3 coolant flows (edited from a slightly different gen4 diagram)

 

nasty!

How fast if flows is hot it is and how much it need to cool.
It circulates mostly to the radiator, so you won't see a lot of movement in the coolant tank.
You might as well change the inverter coolant. It's the same coolant. Quicker and easier to change.