Impedance matching network and power transfer to the load
You have to consider the line between the plasma and the matching network to be itself a matching network if ZO does not equal ZP, its length may have a significant effect on the impedance seen at the driven end, and it is this that you must match into.

For example, for a 1/4 wave line, the transformation will be Zl = Zt^2/Zp where Zt is the transmission line impedance. The math for other line lengths is easy to find but I am not copying it out. 

This can actually be very useful in plasma systems as it allow you for example to arrange for the open circuit at startup to be transformed to a short circuit at the generator to provide lots of volts for ignition.

You may also find reading up on how to drive a "Smith chart" worth while.