Text Preview in v3

I have been exploring the demo of Glyphs 3 and I have been impressed!

I have started by working on ornament fonts in the program and finally tried the Text Preview. I have set up my files as 1000 UPM, 1000 Ascender, 0 Baseline, 0 Descender and the designs often go right to the edges of the bounding box.

I have found that in order to get my designs to display as I expect in Text Preview (with no leading), I need to change my Ascender to 833 (the UPM value doesn’t seem to affect the leading).

If the UPM is changed to 833 but the Ascender is 1000, the Text Preview still shows the default 120% leading.

It seems that I also need to restart the program in order for changes to the Ascender value to reliably be changed in the Text Preview window.

Although it’s possible to change the Font Info back to 1000 Ascender before outputting the font, is there another way to adjust a setting for solid setting in the Text Preview window?

In the Text Preview window there seems to be be a pop-up button (with up and down arrows on a blue background) to the left of the font size. When I press either of the blue arrows I just see a check mark, so that seems unrelated to my leading question. Does that button serve a purpose?

Thank you for your help.

Please read this: https://glyphsapp.com/learn/vertical-metrics