What does a VI have to do with it? Does it say somewhere that Barriers are VI controlled? I only remember the game saying they deflect small, fast moving objects (which is why I've always wondered how shields help with the debris in ME2). So it's a limitation of the shield technology itself, not a VI controller.
A "Shield" is actually a kinetic barrier that is generated by a mass effect generator strapped on the armor.
The shield is not active all the time, it flares up in blue when something like a fast flying projectile triggers an unspecified triggering mechanism.
Said mechanism could be a type of radar, sensor, or perhaps a weaker mass effect "net" that is only there to detect fast objects.
To govern this system, you obviously need sophisticated software, in ME VI's are used for these types of missions.
I theorize that a sufficiently advance VI will be able to distinguish between the passage of air, acts that require interaction with physical objects,
and something like a fast punch or any other melee attack.
Melee attacks are sufficiently different than other lower energy activities, and an advanced VI shouldn't have a problem dealing with them.