Help with custom Morningstar Tristar PWM setup

I am having trouble understanding how removing the load makes the voltage spike. Amps draw goes down.

There is no (or not as much) load now on the inverter so it won't be trying to maintain the watts by raising the amps as much at that voltage.

So by not pulling the amps up as much, voltage will rise for the same watts.

But why does it need the same watts? Why doesn't it all fall together?