According to my OBD scanner, my Fiesta ST with 1,6 liter turbo, idles around 0.4l/h (0.1gal/h), or 0.6l/h with the ac on (0.16gal/hr).
I'm surprised you get almost 9 times more fuel consumption at idle!
Then again, the forester has a 2 to 2.5 liter engine. The larger the engine, the higher the consumption.
Personally I wouldn't bother with start stop technology.
The engine wears out most during startup procedure, according to Shouty Kilmer:
Also, a lot of the 3.6 minutes start stop, is from the entire trip.
Many times, cars stop their engines to start them well within 1 minute. Sometimes stopping the engine, only to start it again within seconds, because that's how traffic goes.
I have never ever waited somewhere for 3.6 minutes (save for a railroad crossing with a long train passing at slow speeds, where I do turn off the engine).
The engine wear, starter wear, battery wear...
Not only the items breaking, but just one time charging labor, nullifies the savings you get on fuel.