All the subtitle size settings in all clients are only effective if the subtitle is in a text-based format (SRT).
They won’t have an effect if the subtitles are in a picture-based format (PGS, VOBSUB).
So make sure to fetch subtitles in SRT format for all your movies.
Or you might have to convert them yourself from image to text (e.g. using Subtitle Edit )
Install PMP additionally and use that.
Switch it into its ‘tv’ mode.
Set its subtitle size to ‘huge’.
Then add a custom configuration file to improve subtitle legibility further:
