You must be mistaken. If someone posts something public (which alot of my photogs do), and I respond to it, it doesn't matter if I have people set to acquaintance, or friends or whatever, they all see it. There are some photog groups I belong to and they are public so if I comment or post, all my friends see it. It's not a big deal, but Facebook deliberately makes things public by default. But there are some "members only" groups I have which are more contained.
Heck even when I post a photo and I tag someone, people I don't know and aren't anywhere on my friend list can see it and comment because of the person who I tagged (his friends can see a photo he was tagged in).
There is no privacy on Facebook. Even though I have everything set to friends and certain people as acquaintances (Facebook makes grouping friends in categories ridiculously difficult compared to G+ by the way), I assume its public info, since people I don't even know can see it.
It's just easier to do my photog stuff on G+ because none of my friends are on it and if I post publicly (which all my posts are on G+) they aren't bothered with it. I have over 1000 people in my photographer's circle, filled with quality posts that I can freely comment on without by friends feed getting hammered every 30 minutes.