silkc2
I've been playing with similar settings, Although I've not found the 'sweet' spot as you put it, I have found a workable form.
I'm running a window width 640 x 360, my layout however is much larger.
I have my computer set to 1920 x 1080 (resolution )
When exporting to HTML5 I use scale and make sure all the scale rates are set to 100
When exporting to cocoonJS the scale is set to 0
Its not perfect but it is full screen. Having major issues with Ipad Retina display though.
I'm eager to see what others add here as well