I have a restaurant cust. that has an above t-bar air handler [Old] no name plate left. TXV slant coil with a trane 7.5 ton condenser. The problem is air flow. When system installed the installer hooked a 16 inch return to to air handler which is way too small. The compressor was changed about one yr ago, before I inherited. My question is; would disconnecting return flex duct and using t-bar ceiling as return, increase the air flow? I believe it would, but before I dive in would like some feedback please.