I don't always buy in to the theory that a player will do much better against another team's reserves. I'm sure it's true against most sim teams and a few poorly recruited and/or coached human teams. However, if a human recruits well 1-12, the drop off to his backups should be mostly due to the difference between upperclassmen and the others. Yes, upperclassmen generally have higher ratings and obviously higher IQs, so there IS a difference - but on good teams I don't know that it's vast enough for a guy to have much better numbers.
Plus, add to it that substitution settings (and the way the sim makes subs) aren't always the same, and you don't always have him facing the backup guys anyway. Their starters may play more minutes than yours or may swap in and our more or less frequently than yours. I guess what I'm saying is the matchups may not favor your guy even if the talent does.