DUDE please stop with your endless strawmen arguments showing that you are an internet expert. Go learn to read and understand things.
So, I'm not sure, what I should learn and understand exactly in your opinion?
Reading and comprehension of what is written. Yeah your technical knowledge is superior to mine, heck lots of people in this thread can make that claim. But I am the only one who asked the OP for clarification of exactly what he was asking rather than assume, because i am not an expert and I am not a mind reader and I do not have all the answers. Reading and comprehension mean sometimes you have to ask questions to better understand what is actually being asked.
The context is for use in an l match atu.
Fwiw my lashup franken doublet is working fine,the atu l match started off with a 1000pf wide spaced air variable,This was ok matching 80+40m but had a min c that was too high,i removed plates untill it was circa 300pf,This works well >40m too 10m,for 40+80m i have 1400 of silver mica caps switched in paralell with the variable,i just thought the vacume cap would alow better efficeincy+ tuning over the fixed silver mica?.The antenna is used mostly for interG nvis contacts,getting on 80m living in a small flat in a concervation area was difficult!.
Now the OP's question was rather open ended, but he clarified things even before you started posting about magnetic loops. My comments were in the context of the above 2 posts. That the OP was building an L match and he had a doublet. Even if you had read the first of those comments, Post 4, before you made Post 5, you would have understood the context of the thread. Again reading and comprehension. Do you use L match tuners in magnetic loop antenna? Not that I am aware of, but they do use a capacitor, not a fixed capacitor as the OP was talking about but a variable one. What is being asked by the OP can be derived from the context of the thread and thus the context of the answers being given.
If you had read and understood the thread, you might have commented in a way that helped the op rather than looking for something wrong on the internet.