this one is called raking. sometimes when you play it's easies to drag the right hand finger across the string and pick the upper string with the same finger,it's usually when the number of notes you play in one pattern are even,so if you 've wanted to alternate picking,every time the whole fingering would change,so it's easier to do this.and it helps to speed up easily when you use your fingers,it's just like a thing called sweep picking for guitar players.so i'd write the right hand fingering like this and the letter r means raking and you'll see that i'd use the same finger for plucking the other string: i m i m i m i m i m i m i m iri m iri m iri m i m i m i m i m i m i m i m i mr m i mrm i mrm i m. and as you saw if you use the right fingering,it'd make you to rake with middle finger for the next fret. start slow and the speed up,continue till you reach the 12 fret