Could work better with some random picture from the fb account itself posted on the group's wall and something like "Check out my other work at [domain name]"? Depending on the group topic, because I personally can't find large and active groups that suits what OP presented in his method and had to join various photography and modeling groups that seems to be active.
So I thought that a HTTP redirect to such url shortners (and I think that adfly has way more advertising power than shorte.st) would allow me to post that link on facebook ([domain name] redirects to adfly shortner, and adfly redirects to subdomain.domain after seconds) and have more succes with it. Am I wrong here?