I think that's mainly the nature of it being an enclosed emitter optic? From what I see the open emitter is typically the window style we're used to seeing mounted on a pistol slide and closed emitter is the bigger box/tube style. Pics below are of closed emitter offerings from Holosun and Acro that seem to be about the same size/shape of the swamp fox optic body.
https://d3apgz7jqdnp73.cloudfront.ne...preset=list720
Above is the Holosun version. I think it's just the nature of closed emitter dots?
Acro version:
https://www.gunsandammo.com/editoria...torial-gallery