[Enchilada]

These are the comments I have on the diameter of this object, however, to my eyes was about 3 to 5 arcsec, and this varies slightly with an O-III or not.

"In regards IC 4191, Karl Henize [in 1962] classed the PNe’s structure, by placing it second in nine-categories of PNe types- Ellipses gradually brighter in centre in order of core brightness. Henize also found the core’s diameter as 6 arcsec, about the size as seen in most amateur ’scopes. Observations from Mt. Stromlo found the outer halo dispersed its light to about 10 arcsec. Henize thought he had seen some elongation, and using the twenty minute photographic exposures, made an estimate PA of 50 degrees. He also commented that he thought the nebula appeared “peculiar triangular shaped.” [which I've never seen, which I assume might be some problem with the optics, perhaps.] This is particularly odd PNe description, but his impression is seen clearly in the image produced in the original paper. In the professional telescopes appears a very faint outer envelope can be seen to extend by some 18x11 arcsec. However, this is invisible in all amateur telescopes. Here IC 4191 remains about 5 arcsec across. Morano (1990) measured the H-alpha diameter as 11 arcsec., finding strong emissions in O-III and H-alpha. This is also especially prevalent within the inner parts of the nebulosity."

Hope this helps.