ALL enlarging lenses of "normal" to sub-normal focal length have falloff. That includes every 150 with
4x5 film. Even a 150 taking lens for 4x5 has falloff. That's why one hypothetically needs a different
ground diffuser for each different lens. This is compounded by any potential uneveness in the mixing
chamber, as well as increased fbf near the edges of sheet film. Of course, we just get used to burning in the sides & corners etc, unless you're printng negs with a reasonably matching degree of density loss in the corners. No big deal unless you're working a process which requires truly even illumination each time. But it is a fact of life.