I'm seeing a difference between using the standard_surface IOR and using the complex_IOR node. The facing value seems correct, however the values start to differ when approaching the edges.
standardsurface IOR 1.5:
https://www.dropbox.com/s/pi6w7y9aavxirk0/diff_standardsurfaceIOR.jpg?dl=0
complex IOR:
https://www.dropbox.com/s/278yyug34mbmn5s/diff_complexIOR.jpg?dl=0
The images show the standardsurface with spec only, roughness to 0, spec color 1 and a constant white dome env & the complex IOR with n 1.5 and k 0 directly connected to aiUtility in flat mode.
KtoA 2.0.5.0 / Arnold 5.0.1.5