It cant be improved with the options to align to x-height and cap height:
https://illustrator.uservoice.com/forums/333657/suggestions/35039683

Simon, can you explain it further, with images?

It could be improved by making it work accurately. Currently, that is not the case.

This should be also extended to the set of 'Convert to Shape' effects!
E.g. 'Convert to Rectangle' is a great way to add a live background plate under a live text, but it is applied to the em-box, naturally. If you introduce 'Tight Fit' option there (along with 'Cap-height' and 'x-height'), this would give much more control over the parametric appearance workflow in Ai.

Follow-up to the previous comment:
and if you make a stroke instead of a fill, enable Preview Bounds, you will have a strange gap between visual edge of the stroke and the bounding box. And the green rectangle will align to this enlarged bounding box! With bbox excluded it will align to the black fill again.

So, here's the problem.
I have a live text, and it has two fills. Bottom orange fill has Offset Path effect applied to it.
For whatever reason I want to align my green rectangle to the visual bottom of this text (I marked it with a guide).
1. I see that a bounding box is now around my Em Box, and lower edge is lower than the guide.
2. So I go to the options and enable 'Use Preview Bounds'. Ai extends the bounding box so all orange is now inside of it, but the bottom edge is still where it was — because Em Box is still higher than the orange fill.
3. So I go the options again and check 'Exclude bounding box: Point Text' — I believe that it would trim that part of the bounding box that extends below the orange fill.
4. I set the text as a key object and align box to the text.
5. Boom, it aligns to the black fill!
6. OK, I say, I go to options again and untick exclusion.
7. Now it aligns to the bounding box!
Having Preview Bounds off and Exclusion on will align to black fill.
So there is no way to align a box to a visual edge now :)

It took me a while to find the option.
Well, I found it at first try, but it's named differently now and has two options, so I wondered if there's a different place for a Tight Bounds now.

It clashes now with 'Use Preview Bounds' options. Please check all combinations and see for yourself (especially text with a fat stroke, 'Use Preview Bounds' on, 'Exclude bounding box: Point Text' on — is should align art to the visible edge of the text's fat stroke, but it does not).