I think the easiest way to explain the issue thinking of air as a fluid. Your room is sort of like a river with the outlets from your HVAC continually circulating to the returns (ceiling or lower wall usually). That river moves through continuously normally unless you use plexi glass. Then it acts like a little dam a beaver builds in a river. Soon there's a build-up behind it that's slowed and no longer moving as efficiently downstream. In that pocket behind the dam you are building particles potentially up that are not moving as well through where the air filtration system hopefully captures some of it.
Every time I see teachers putting up shower curtains and plexiglass barriers I want to scream at the screens... At some point I need to find someone to actually run the models visually to show people.
The only place the plexiglass barriers do have efficacy is in a checkout/front desk type situation.