It should be the same- please check if you have a cross port leak of the MCGV...
You can do this by setting the flow to 100% the channel you want and pull out the bottle filters from the liquid of the other 3 channels...Do you see air being pulled up in the other 3 channels? If yes, then you have a cross port leak,
Also, if you take the adaptor into the active inlet valve from the isocratic pump and move it to the quaternary pump -so bypassing the MCGV (where you have 4 lines in and 1 out) how does the pressure look?
Thanks Jhagel, the advice was helpful