Practically speaking, I'm not sure how you'd roll up/unroll an additional cover with an automatic cover, unless you used something like a Solar Stick so that the bubble cover was manually removed every time you opened the auto cover. I'd expect that might be something of a hassle.
Rough rules of thumb on heatloss suggest about 70% is from evaporation, 10% conductive (eg cold ground) and about 20% radiant.
You're covered, so to speak, on the evaporation for sure, and probably some of the radiant
I am in Michigan and this year have been experimenting with winter operation via an air supported dome (Ameridome.)
On an autumn average cold night in the 30s, even before I installed the dome, my 12 mil bubble cover lost an average of 6 degrees during 12+ hours of having the heat off -- that's with an air-water differential of 30-odd degrees to 94 degrees. Now with the dome and middling 30-40 degree temps, I'm losing more like 4 degrees per 12 hours with no heat...so about a third of a degree per hour. That's likely to change soon though when daytime temps drop below freezing
Depending on your temp differentials and your tolerance for heat bills, plus the BTU rating of your heater, you might in theory find it economically worthwhile to have an extra layer of insulation against radiant heatloss if you can stand the hassle factor. If you run some experiments and calcs and decide to do this, I will try to dig up the thread on how to make your own solar stick and then show you how I made mine to be rolled "in pool" using a marine grade rope through two cellular ABS tubes.
To calculate heat loss, you need to know:
Heat differential (air/water) x surface SF of pool x 5 BTU.
You then need to know how many BTU it takes to move your gallonage of water 1 degree in an hour with your heat to make sense of the answer.
For example, at 24,000 gallons, my 266 BTU gas heater needs roughly 200,000 BTU for 1 degree (80% efficiency). So at 212 BTU/hr, I get a little over a degree an hour in ideal conditions.
Here's a pic or two of my winter "in pool" solar cover that might work in the case of an autocover:
The bubble cover is attached to the cellular foam pipe with automotive fasteners in drilled holes. You hand roll it while standing in the (warm) pool water. I then use another marine grade turnbuckle hook on a line from my diving board to open 1/2 section for physio therapy, or use a bungee anchor I set up to hold the entire roll, both sides, off to the side. In this way, with an injured knee, I don't have to bend or fool around on the deck in the cold at all
