I installed a test install of SMF there is no issue that I see.
Now with SMF there is no cookie settings persay other than the name so Photopost must be on the exact domain other than that there is no fix for me to post as I do not see an issue here.
If SMF is on www.domain.com
then Photopost must be on www.domain.com
The SMF cookiename must be entered in Photopost settings other than that until SMF gets wider cookie settings nothing else I can say here. I dont see any issues on my test installs.
The only thing I have seen on your installs as I believe I point out to everyone about cookies is to ensure your domain is not switching