about how tall?
About as tall as the uppercase letters, I'm also not sure how possible this next suggestion would be but the lines could also be thicker for it.
Perfect!
Same for . , ; of course.
It's an abbreviation for "pointy-headed."
x@X So in this font, anyway, the @ is uppercase height.
x@X
So in that (monospace) font, the @ is uppercase with descender, the full available height, like parentheses
(@)
It also isn't circular; it's taller than it is wide. Does that help?
good?
That seems to overlap with other glyphs, so can you try make it narrower?
However, in my opinion, it's good 
It doesn't overlap, just touches. I can't make it thinner without making it look ugly.
I cropped the image to isolate the symbol. It's pretty good, I like it.
It's funny how just scaling the symbol up on the y-axis can make it look so much better.
I modified the symbol for you so it won't touch other letters:
The symbol is COMMERCIAL AT (U+0040).