Length of main rebar in concrete pile

Dear All

I run an example in my model as shown below, 7 circular columns embedded 1.5’ inside the cap, and the length outside is 12 ft. (Total length is 13.5’). Why should the main bar be located along the entire length of the column. When I changed the distance “FROM” to 0.25’, or the “TO” to 13 ft. to account for the concrete cover, I got an error.