Modern front derailleurs aren't designed for half-step gearing as the inner cage plate is too deep to clear a middle chainring nearly the same size as the outer unless the derailleur is mounted way too high.
Half-step was more common when 5 and 6-speed freewheels were the norm as it filled in the big gearing gaps between the cogs. With newer 8, 9, 10 and even 11-speed cassettes, the need for half-step pretty much went away and current front derailleurs won't work with it.