Unless you have very fine-tuned spherical falloff zones, it is very hard to make the fingers move without interfering with each other, adn/or the hand. One solution you might want to consider is setting up each finger with an extra group, such as a knuckle, to "isolate" the fingers from the hand, more or less like the buttock groups on figure "isolate" the thighs from the hips to minimize distortion. That way, you can work without spherical falloff zones entirely. All hand poses only involve settings for the "known" finger parts, so the knuckles will simply be "along for the ride", doing their bit to make sure the first finger joints don't distort the hand. Give it a try if you think it's a workable idea. Good luck.