Pressure drop in the reservoir can be a result of many reasons, you mentioned that the two layers are not in communication (350 m apart)
- Initial GIIP of each layer.
- Cum. production of each layer.
- Permeability of each layer.
- Transmissibility (which is a reflection of permeability).
- Facies distribution (Layer continuity).
- Existance of aquifer.
- Reliability of reservoir pressure measurment.

every point of the mentioned can be discussed in details and it is depent on the case.

Regards