the shadowsense setting works a lot like the anglesense setting for lights.
it affects how quickly a face becomes dark based on the angle the sunlight2 is hitting it.
this only has an effect if there are many faces that are on slightly different planes (ie: tri soup terrain).
on a flat floor, with walls around, shadowsense has very little effect.
ex:
shadowsense 0.0
shadowsense 0.9

regarding less shadows from main sun, yes, i agree it is an issue.
the problem is that the fake GI is too dark in general, which means i had to use brighter sunlight2 settings which hides the shadows.

maybe some more tests with higher number of suns with even lower sunlight2 or something may yield better results...