The potential between the control grid wires is not the same as that of the grid wires themselves

For example if the anode potential penetrates between grid wires we have a higher potential.


Source:


Fundamentals or radio-valve technique - Deketh - Philips Technical Library


Perhaps and slangy could be:


One is walking past a bus stop. There is someone smoking 5 meters before the bus stop sign and someone else smoking 5 meters after the bus stop sign. The walking person may find a convenient place to breath fresher air inbetween the 2 smokers ie near the bus stop sign.