Hey! Need help)
I have the HTML video DOM. And added span-DOMs with text as preview of subtitles for users. I have use different custom fonts (google fonts).
I have set font family/size/color.

So, after that I have created the ASS file with PlayResX/PlayResY as size of HTML video player and write font size/family and color.
But after I have created video by FFMPEG with my new .ass file - a font size is smaller that in HTML.

If I understand correct- the correct values of PlayResX/PlayResY should resize a font size to correct value. But it's not.

For example, I use font size = 18 px. Video resolution (original) = 608x1080. My HTML video player have 286x509.
So, in .ass file
PlayResX=286
PlayResY=509

FontSize=18

but after genereting - I have not correct sie in video.
I have tried to understand the addiction between sizes. And made some tests in Aegisub. And found the correct font size in my example (for current font) = 44px!
I don't understand addiction......