From what I read and what I use an IC with Steel = Modified with lead, A Modified with Steel = Full with Lead and the IC was used over blocks or decoys as you are within a specified range.

If you do like I do, I place landing spots and my farthest decoy is no more than 35 yards. Made a heck of a difference for good killing shots with steel.

My IC just patterned better in my Benelli - I found it hard to believe too but I that is what patterned well.

JW