Need help with RO solenoid shut-off

[Delphinus]

I have rearranged my topup for my tanks into a single reservoid auto-fed by the RO unit. Problem is the reservoir is now 30 feet "downstream" of the RO unit (I used 1/4" line) and now the shut-off doesn't seem to shut the RO unit off when the reservoir is filled.

It works fine when the output line is about 6'-8' or so. So I'm guessing that what's happening is the pressure takes a LOT longer to buildup in a 30' section of line over a 8' section of line (the solenoid works off pressure .. the pressure builds in the output line once the float valve is shut, the pressure moves the solenoid and shuts off the intake to the RO.)

So here's the question. Does my theory seem reasonable? (I had contemplated using 3/8" line instead of 1/4" because I was worried the line was too long, but if my theory is correct, the 1/4" is still better because the 3/8" line will take even longer to build up enough pressure to shut off the RO).