@MichaelMouse
Your photo proves the point. You end up with a 3" diameter foot. It works well for the large bowl in your photo.
You know by now the discussion is about small bowls so assuming you are not just being a troll I'll try one more time.
The discussion is about small NE bowls where the 3" foot is way out of proportion.
It comes down to what we perceive as esthetics If you like a 3" foot an everything regardless of size that is your choice.
As long as the 3" hole for the recess is part of the design it works.
I like a smaller foot on smaller bowls or no foot which is my favorite especially for larger functional natural edge bowls.
Can't see the difference in the diagrams, where you have to start your bowl tenon shoulder above the edge of the mortise, I perceive. "Just for you," I include a a demonstration of a mortise inside a tenon, to show that your contention that you can't go thin and bark up in the same piece, and you still don't get it. BTW, 2" plus maybe a quarter larger each size for the "foot" makes 2 1/2. You want to argue style, I want to present substance. Can't help YOU, possibly influence others to think creatively and not fear a perfectly useful concept. The open mortise no-foot form sitting on its 2" (or other) base is also my preferred way of conveying lift. It's just that I like to have folks use the bowl or plate rather than chase it.
You know there are 1" dovetail jaws, or do you? If you're working small, they do a nice job of staying small. The little dark maple wood chip dish was ~6" long and maybe 2 wide with a 1" recess. As a matter of taste or style, you use what's appropriate to your objective, though sometimes it looked better in your mind than on the table. This is a bit over 10 with an inch and a quarter base. Obviously there's an inch or more of thickness on the bottom to keep it from tipping over. Now if only it had looked as good in person....
In any case, newbies, remember that a set of dovetail jaws give you an excellent hold when you realize that they don't "grip" anything, just wedge the nose up against the bottom of the mortise as they expand. I believe the key to use of ANY hold, innie or outie, in maintaining circularity and position throughout, is to use support from the tailstock for as long as possible. Also safer, because even a horrible "catch" won't send the piece up into whichever portion of your anatomy you may have in the way. Which, incidentally, can oly happen if you are UNDER the wood. Cut above center on convex, below center on cncave surfaces, and there will be air there. Use the gouge properly, like this (c and it cannot catch, right Jamie?
If you have a Nova chuck and just HAVE to have an external hold, I suggest the "75mm" set, which are actually larger in outside diameter, but can hold a 1.8 inch spigot or 1.3" (standard 2X) square.