In case anyone follow this, I'd like to add a couple of pics of the filter data.
And for my own reference.

Hi Cassius987!
I'm not sure this is right. Maybe you're thinking of the power just over
the cap alone. The power over time is zero, since it gives back the same
amount of current as it stores over time. It's the current and voltage is 90deg out of phase

But, what we have here is adding voltage to voltage from the neck PU to the bridge PU. If they are 90 deg out of phase the sum is far from zero.(se pic the purple curve is the sum)
In fact, the only time we have a complete cancellation is 180 deg out of phase,
If you have 0 deg (= in phase) you would double the output signal.
In the pic the purple curve is the sum.

Please let me know if I'm wrong here!

I think you're just saying what I said--albeit with more detail--correct me if I'm wrong? I read your post and agree 100%, it's what I was trying to get across with what you quoted. I think where I may have erred from your perspective is mentioning cancellation in zero degrees phase (which is the norm) although what you may not be thinking about that I was is that due to spatial differences in the pickups there are some frequencies that do indeed cancel and some that add together like you said. Thanks for adding to the discussion.

Any 360/12c63 owners out there!
Have anyone tried to measure the cut off frequency (calculated to 273 Hz)?
Would anone agree to my calculations earlier in this topic
Do you have 330k(neck)//330k(bridge)//500k(blender)-all parallel? (would be total 124k)

Keep posting!
Thanks!

Unless I missed it, nobody has mentioned that the input impedance of the amp will affect the cut-off frequency. An amp with a lower impedance will cause this frequency to rise, as you are trying to draw more current through the capacitor.

Another reason we all like tube amps: the input impedance from jack straight into the grid of a 12AX7, whatever impedance that is, is an optimal impedance for jangle.