Font size and style in formulas

When editing formulas in a text editor, the font size is unstable. I use the 14th font, but when I start typing a complex formula with fractions and indexes, the font size decreases significantly, even if it is still the 14th. Moreover, if you type Cyrillic letters in the formula, they will not visually resemble the rest of the Latin letters in style (at least, italics do not apply to them).
I use the latest onlyoffice (desktop editors) on Win10 and Linux.
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