Bench Bleed Master Cyl Question

Rebuilt my original Duster master which I had re-sleeved. (front disc / rear drum). I'm trying to bench bleed it but I get nothing from the front reservoir tube (the smaller reservoir that services the rear brakes). No air, no fluid. I'm definitely skeptical of the residual pressure check valve,which my FSM said to install in the "front" reservoir. Obviously a spring-loaded rubber plug sealing the port would prevent anything from flowing through it.
My gut tells me all is OK and it's just some weird design thing, but I wanted to ask about it before installing the master on the car. Thanks for your thoughts

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