Size subtitles on Plex


My system:
Plex Server on iMac
Plex Client on Apple TV 2 with aTV Flash (black)
Original video is 720p (mkv) with the same name in file “.srt” 

I have a question about size subtitles on Plex. The size is BIGGER and BOLD.

Can I change the size of text or maybe there are any hidden settings on aTV Flash (black) ?