I must be missing something on how groups (S2 system, new app) work...please tell me how to do it right! 

I have about 12 sonos products in my home.  Often, I run most of them in a single group called “inside” which includes all but 2 of the products.  I group them together using the “inside” group.  In the evenings, I want to cut it back to just 3 of the products, so I try to select just the “small” group, but that just turns off those speakers within the “inside” group.  The only way I’ve found to reduce the number of speakers in a group is to first click “everwhere”...twice...first to select everything, then to select nothing, then click the “small” group.  Well...I suppose I could “uncheck” 8 speakers one at a time too...but that’s seems silly when groups are supposed to make this all easier..

So much fiddling can’t be right!  Please tell me a more efficient way to do this.