Can you make do with a standard swing arm mount? I think it would reach far enough if you have the vertical clearance for the pole stand.

I love this one, even bought an arm extension for it.
https://www.amazon.com/Desk-Mount-LCD-Tall-Po … e/dp/B00689HXI4

Not cheap, but oh so robust and very flexible 'settings'... 😁
The arm can be mounted anywhere on that pole, so for your purposes it'd probably be at the bottom.

Granted, it has no telescopic(!) arms, but I cannot imagine such a thing would exist (all that friction inside the tube when heavy monitor on the far end..?).

Is lateral shelf space the problem here, or....?

PS: the short pole version is $30ish cheaper, if you don't think you'll ever need that xtra height flexibility.
https://www.amazon.com/LX-Desk-Mount-LCD-Arm/dp/B00358RIRC

It doesn't have to work exactly like I've drawn, I just need something that can put the monitor in those two positions & can easily be adjusted on the fly. 😀 Something like ^^ that would work fine (but man it's expensive! Get what you pay for I guess.)

As long as the arm extension is enough, I think something like this would be good for you. The knuckle by the monitor allows vertical tilt and the pole allows height adjustment.