NEC-LIST: Coax, Skin effect or Proximity effect ?

Hello all,

Excuse me if this is a bit off topic.
I have a very basic question.

It is said that Loss of coaxial cables has frequency dependency
due to skin effect.
The inner conductor has current concentrated on the outer surface,
and outer conductor on the inner surface.

Here, I encounter a basic question:
"when the current is concentrated on the INNER surface,
 is it due to skin effect ?"

Obviously, the current is on the INNER surface,
because there is current in the inner conductor.
So, isn't that due to Proximity effect ?

How about the inner conductor ?
Skin effect and Proximity effect mixed ?

If so, is the loss proportional to the square-root of the frequency ?
(I believe resistance change due to Proximity effect is different
 and stronger than the square-root of the frequency, but not sure.)
If so, the fact that actual coax cables show square-root dependency
is because Proximity effect is masked and dominated by Skin effect ?

I would appreciate any related info.

Hideho YAMAMURA. //

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