I'm playing a gig that requires some really EXPOSED arco thumb-position passages, including an eighth-note passage that begins with a fourth interval (E-A). After the "E", it's bassically a scalar thing in A minor. I've tried a couple of ways to finger the first interval: Using my index and middle fingers for the E and A respectively (on the D and G strings), and holding both notes down simultaneously with the thumb. The latter solution seems more elegant, but the tone really sucks (my strings are on the high side, and I have really stubby thumbs). With the former, intonation suffers and there's a clumsy shift. Any hints?