How much air should be coming out of my defrost ducts

[Sixt8Chrgr]

This subject probably sounds goofy but I have to ask. I just restored my heater box with AC in my 69. Prior to restoration the heater core leaked so the heater core was bypassed therefore I never ran the heat/defroster. Now with everything up and running when I select the defroster option I just get a little air from the ducts. Just barely enough air to feel up through the ducts. However, the air blows good out of the heater vents while the defroster is selected. And blows well in heat mode. All the other functions work as they should. I read in the FSM that there should be 30% bleed through the heater ducts while in the defroster mode. But seems to me that I have like 90% bleed through the heater ducts while defrost is selected. Should I adjust the linkage to open the defrost ducts more or is this normal? I just don't have a baseline since I never ran heat/defrost prior to resto. Is this normal?

Thanks