AC Vents Issue

[Lurayfarmer]

Today I finished installing a new radio and AC hoses. I opted to delete the long second AC hose to the center vent using a plug set from a vendor. A single hose to that vent seemed adequate. I cranked up the AC - and found nothing at all coming from the center vent. The hose is on tight, and when I lift off the plastic nozzle from the main manifold there is cold air coming out.

My guess is that the double hose was used when some GM engineer discovered the same problem using a single smaller diameter hose for the center vent. Air coming up from the blower looks for the easiest exit, and that's the main AC vents which have a larger diameter.

Anyone else delete the second hose to the center vent and get this issue?