I'm about 6' 1" these days; in my youth I could stretch my neck and get to 6'2". So I'm tall-ish, but not unusually large. I have a pretty small frame for my height - I wear a 43" jacket and 33" waist on my slacks. I know, TMI from The Shrike . . .
I've got a convenient piece of wall here in the office where I could measure my "elbow reach" reliably.
From sternum to elbow, I max out at 21" with my arm straight out.
Then I made my elbow larger by putting on my jacket. The "larger elbow" increased the distance to just under 22", which I would consider statistically the same as Sweaty's reported estimate for Patty. Finally I shifted my position about an inch (to simulate the inability to pin down the exact location of my spine relative to my elbow) and I got to just over 22". Even closer.
So then I measured my elbow reach with my arm forward, as the dance instructor's appears to be in Sweaty's latest photo comparison. I got 13".
I next twisted my body back to create the impression of foreshortening when viewed from behind. This got me to 9".
Your body dimensions are pretty similar to Bob's, Shrike....and, to mine also.
I'm 6'0" tall, and with my arm straight out to my side, fully horizontal, my elbow-reach is the same 20".....as yours and Bob's...(give or take an inch)...
In the graphic above...I made measurements for Bob's elbow-reach at 15-degree intervals.....and, at the half-way point...(45-degrees)...his elbow reaches about
17-18" away from his spine.
If you measure your arm at that same angle, I bet it'll measure
almost exactly the same.
But, your elbow-reach doesn't come close to matching Patty's....when yours and Patty's figures are compared
at comparable arm-angles.
There is one important factor that I didn't include in my comparison from earlier today....it's the 'correction factor' for the
angle-of-view, of both Patty and the Ballet teacher.
In the graphic above, with Bob, I
did include it for Patty....(using a modest estimate for the 'angle-of-view', of 25-deg.)....and the
apparent length of 19", for her elbow-reach, adjusts to it's
actual length of
21".
If I had applied the 'angle-of-view correction' in my earlier graphic, Patty's elbow-reach would adjust
upwards...to approx. 26-27".
Likewise, the woman's elbow-reach would also increase, by a few inches.
Her arm is out at a greater angle from the body, than Patty's is....and greater than 45-degrees...so her elbow-reach, at that angle, should be
close to it's maximum.
So there you have it. A tallish man with a smallish frame can, depending on the angle of measurement and the apparent bulk of his elbow demonstrate a similar "elbow reach" to that SweatyYeti is claiming to measure on Patty. However, my controlled measurements here in my office also varied by 13" as a function of the angle of my arm forward-to-back.
I don't think that's an accurate statement, Shrike. I think there must be an error, or two, in your figuring.
One error, for sure, would be due to the missing 'angle-of-view correction factor' for Patty, in my earlier graphic. (Sorry about that.

)
So the potential error has an enormous influence on any apparent measurement like this without precise control over the angle from the body and the position of the arm front-to-back.
It's true that there are many different combinations of angles, that the arm can be positioned in....but, this is still pretty
basic geometry...and there's a lot that can be determined, with a high-degree of accuracy, in measuring the arm/elbow positions.
In other words, the arm and elbow positions, and their measurements, are not as 'chaotic' or 'nebulous', as one might think they are, at first.
This analysis just needs to be
expanded on, more...that's all.