Structural Engineering: Distribution Width for Concentrated Load on Concrete Wall

I’m designing a C.I.P. concrete cantilevered retaining wall. I’m trying to find the distribution width for a concentrated load at the top of the wall. So far, I’m unsuccessful. In masonry, it’s called a “flush wall pilaster” and there is clear direction if the wall is masonry.

Is concrete the same as masonry in this regard?

T. William (Bill) Allen, S.E.