personally i wouldn't go out and buy whole bunch of effects first to get more sustain. sounds like you just tapping the string as hard as u would on the lower frets as u do on the higher. the higher frets need more pressure to sound out. trying working up muscle in that tapping finger. (yes as lame as it may seem do finger execerizes) then u can tap harder and get more volume.

then i would go get the effects.