[Amps] RF voltage on VHF strip line

[N1BUG]

So, moving along from the topic of screen grid voltage regulation 
and direction of current flow, here is my other/next question...

Suppose you have a 4CX1500B sitting in the middle of a half wave 
plate strip line for 144 MHz. Some may prefer to think of it has two 
quarter wave lines with the tube between them. This is a "teflon 
sandwich" line where the upper brass plate is connected to the tube 
anode, the lower is not. The lower brass plates are grounded at the 
far end from the tube. Between the upper and lower plates we have a 
thin sheet of teflon that forms the dielectric for the DC blocking 
capacitor.

Can someone help me understand whether (and if so why) there would 
be significant RF voltage across the blocking cap? Obviously RF 
voltage is going to vary along the *length* of the line, being high 
at the tube and near zero as we get toward the grounded end. But 
what about voltage across the teflon sheet between the upper and 
lower plate *at any given point along the line*?

I am trying to understand WHY this thing would want to arc or break 
down only when RF is present. My mind wants to believe that the RF 
voltage across the capacitor at the point where the teflon shoulder 
washers insulate the screws holding it together would not be 
significant, and that the voltage would be just B+ regardless of 
whether RF is present or not. However I see evidence this is not the 
case and want to know what it is that I don't understand.

73,
Paul N1BUG