Columns and beams: to trim or not to trim?

[patricks]

I have several wide-flange steel columns and beams shown in a building, and in some places the beams trim back from the column when the beam endpoint is at the center of the column (which is what I want it to do) and in other places the beam goes all the way to the center of the column (not what I want it to do). In all cases the top of the column and the top of the beam are at the exact same level. How does Revit decide to handle these situations, when to trim the beams and when not to?