Do you have checked whether the tv-viewing-area is different than the computers, i. e. the tv-viewing-area is possibly zoomed closer?
Check the tv-settings or the manual, if there is a kind of automatic mode, which sets the picture correctly.
And who delivers the tv-picture? An attached external hard drive, a mediaplayer, a laptop and a softwareplayer like VLC?
This limits the options you have to correct this.
You can also change the format of the subtitles, so that you can force the display height. I guess you usually use .srt-subs.
When you use .ass instead then you can set the height in the header.
But that means, for each film you want to look at the tv, change the subtitles. This is not very comfortable.
"I don't believe in God. I just believe in Billy Wilder" - Fernando Trueba