WF,
Thanks for the pic..
I recommend a real spillover, but not a constant running spillover..
Basically here is how it works, using a single pump, filter, and heater.
In the Pool mode, water is sucked from the Pool by the pump and then pushed through the filter, heater, and back to the Pool..
In the Spa mode, water is sucked from the Spa by the pump and then pushed through the filter, heater and back to the Spa..
In the Spillover mode, water is sucked from the Pool by the pump and then pushed through the filter, heater, and back to the Spa.. Obviously, more water going into the Spa than coming out makes the Spa spillover into the Pool..
The advantage of your current system is that you can use the Spa in the winter with all the pool plumbing shut down. If you normally do not close for the winter then that is not much of an advantage.
One downside to a constantly running spillover is a constantly increasing pH... We normally suggest that you use your automation to schedule the spillover to run for 30 minutes twice a day. This keeps the spa water fresh and it would be saltwater... You could still push a button and turn on the Spillover any time you wanted to show off..
Thanks,
Jim R.