I agree with all the comments above. You need to consider the ability to fill the mould cavity and then feed.Perhaps only a small section of the casting has thin wall casting. If the thin section is separating 2 thick sections you have a potential problem on hand. May be a casting manufacturer can help you more. Else approach AFS or Investment Casting Institute, who are always ready to help.
"Even,if you are a minority of one, truth is the truth."
Mahatma Gandhi.