Subscript (and superscript) size seems too small?

[firai]

Thanks for the effort in adding OpenType Math tables to the font! However, it seems like subscripts (and superscripts) read noticeably smaller than other math fonts, especially on paper. The difference seems to enough to make the subscripts a bit hard to read in Noto Sans Math.

The following screenshot shows the effect printed to PDF from Microsoft Word with all fonts set to 12 points, but the results from XeLaTeX seem to be similar. The height of the regular-sized ε is essentially the same between Noto Sans Math and Fira Math, but the height of the subscript u with Fira Math is about 16% larger than Noto Sans Math. (I probably should have used exactly the same letter in the regular symbol and the subscript, but hopefully it doesn't throw off the comparison too much.)

It seems like this is mostly caused by the script size set in the math table. Noto Sans Math seems to have the script size set as 60% of the regular size, while the setting for other fonts are around 70-73%. The second level script size also seems to be a bit smaller than other math fonts.

I also don't know whether there may be other contributors to the visual effect described above, such as x-height?

Noto Sans Math

Fira Math

Lete Sans Math

STIX Two Math

Cambria Math