Setting Boundary Conditions in Toughreact

Hello All

I know how to impose Dirichlet and Neumann conditions for a single column volume like A in my sketch (one dimensional case). In the image, the blue cell represents a injection block.

But when i try to do the same in a volume like B (multiple block columns), under flow conditions i observe overpressure in contrast with the one dimensional case. What changes from the one dimensional case in Toughreact ? What i am missing?

Thanks in advance.

David