Yeah it's difficult to judge. I'm not saying it's 100% sure that it's coming from inside the circle or the outside of the circle. Or perhaps there could be a combination. What the thickness of the plume does suggest is that even if there is some exhaust coming from the sides, it's not uniform, and some parts of the side wall do not seem to feature any exhaust plumes.
Coincidently, Mk41 vls has 569 mm inner cell width. Diameter of Tomahwk missile body is 520 mm. So, assuming there's not an piece of folded fin protruding outside of that diameter, there's still roughly 25 mm of clearance between the missile and the cell wall.
You're going to have to figure it out with computational fluid dynamics.