You haven't entered into your profile where you are.
It's hard to say, what the code for your area, would say.
You should have more support at the foundation for your posts, such as you have mentioned.
You could contact your sip provider and get their recommandations for sip support. Most like some direct bearing on the foundation.
You might be able to get away with making a 10" thick wall for 2" of support for your sip if the sip isn't going to carry any vertical load. If it is going to carry some load then both sides of the sip have to sit on the shoe at the foundation.
See if the sip company has a foundation detail drawing, most do.