Are you starting this with
xmodmap ./.Xmodmap
?

If you were to use Emelfm2, you should be seeing a file under
/home/user/.Xmodmap

If you were to open that file, it would only have this one line written in it.

keysym F7 = Tab Tab Tab Tab

(Sorry, I guess Tab shouldn't have been spelled out in all capital letters)


Anyway, I'm really probably one of the worst persons here to talk about such a thing because I can't seem to do anything right on my tablet.

I'll let someone else take over from here.