Oh so you've got some stone to lay in a band or something around the columns I take it -- if so you want the block to be an inch or so smaller each way so that the transition happens in an inside corner -- fours will work fine for that and still give you the solid grout concrete center it's a little harder to lay a four and keep it plumb -- I think I'd still go with eight by sixteens (actually 7 5/8"s x 15 5/8" and lay then with no joint between them to make them as small as possible, then dry lay whatever brick you are using and open the joints a hair to -- if you can even get 1/2 inset, you will hide the back of the stone on an inside corner -- if you cant get enough like that you probably would be happier with the fours and trimming a little off of them to get the desired inset
