It is going to be difficult to make a consistant sound when your up stroke is a fleshy finger tip and the down stroke is a finger nail. Maybe the answer for consistant finger sound is to work on actual finger picking, where you exclusivly use your finger tips, mostly with up strokes. This is much more difficult to learn, but the notes will at least sound consistant. This technique is used by many guitar virtuosos, both accoustic and electric. This is an advanced skill, but maybe this is what you are looking for.