It is not the amount/number of frets but the how to do it.

I hope I read your question correctly. These 2 exercises should help you get started.

Try this "pattern". It is a 1 string pattern that you can move to any string. It should apply the basics behind the tapping.

Tap (t) the string on the marked fret (the 12th fret in the middle) with the pointy finger of the pick hand.

Pull off the string with the same finger to ring the open string.

Hammer on the next note with any finger of the fret hand at the designated fret-- 10.

Repeat the tap, pull off, hammer on following the pattern of 12- open fret designated note.

This exercise is based on major scale pattern. WWHWWHW

El--12(t)--0--10--12(t)--0--9--12(t)--0--7--12(t)--0--5
Bl-----------------------------------------------------------
Gl-----------------------------------------------------------
Dl-----------------------------------------------------------
Al-----------------------------------------------------------
El-----------------------------------------------------------


El--12(t)--0--4--12(t)--0--2--12(t)-----------------------
Bl-----------------------------------------------------------
Gl-----------------------------------------------------------
Dl-----------------------------------------------------------
Al-----------------------------------------------------------
El-----------------------------------------------------------

After you have this down move the pattern to different strings.

Try this exercise next after you have the top one down.

Any string l--12(t)--0--10--12(t)--0--9--12(t)--0--10--

l--12(t)--0--7--12(t)--0--9--12(t)--0--5--12(t)--0--7--

l--12(t)--0--4--12(t)--0--5--12(t)--0--2--12(t)-9-10-12

This should supply you with the ammo. Now apply the principle to linear scales and "tap -tap- a- rooh"--What Movie?

These are just very basic licks. They are not EVH material but should provide a solid foundation for you to learn on.

Good Luck and Rock on!