filing nut slot down

I don't have much experience with fretted instrument setup. I have a Kala sop, that Ive took the action down at nut a bit , with nut files, but not sure how low I can go. I do play barre chords at 1st , and would like to go further down. Is fretting at 3 ,, and a business card stock being at 1 under string and having just a bit of resistance apply here??

Assuming frets are level, yes. Some go even lower, matching the low of the slot to the top of the frets.

thanks Kekani !

Check out " Frets.com " lots of great info.