Custom Ascender for particular glyphs

I am setting a custom ascender metric for x y z glyphs.

At the moment, I have two Ascender parameters, one positive and one negative:

Ascender 500 “affect x y z”
Ascender 800 “affect all except x y z”

I would like to get away with this, but it makes x y z glyphs have an 800 ascender:

Ascender 500 “affect x y z”
Ascender 800 “affect all”

Is this possible?

The reason is that I do not want to have to edit two parameters when adjusting which glyphs are affected.

Why do you need an ascender so low?

So I, in a font with an italic angle, in the glyph parenright, can rotate the parenleft component 180° while still keeping it vertically balanced, while having auto-alignment activated.

I am setting a custom ascender for subcategory parenthesis.

Does this make sense?
I am attaching some images to make it a little bit clearer.

If you have a better solution, I would be happy to hear.

this is not controlled by custom parameters any more but by Metrics:

And use a “Body Height” instead of the ascender.

Thanks a lot!

I meant to say that I was using the Metrics, but the Body Height seems to be exactly what I was looking for. No need to even add Scope then.

Thanks again, for both the response and the feature, very helpful!

I found another solution. Add a *origin anchor to the base glyph. It is a bit tricky to know where to put it. Add a guide to the origin point {0, 0}, (not where the left side bearing hits the baseline, a bit to the right from there). Then set the guide to the italic angle. Add the anchor on that line and move it down. For me it was -151 unites.