Haven't you ever heard Brad Christian before?
Their was once a guy, whose hands were so small you could see the card sticking half way out, but his misdirection was so good no one ever noticed. So no, the size of your hand or the way your fingers are does not matter much in palming. It is all about misdirection.
If you don't pay attention to yourself palming, your audience won't.
Also, if you are not very well informed about misdirection and how to control an audience, I suggest picking up a book on it. Now... if you do not have the money to purchase a book, or do not want to take the time to learn, I suggest learning Tenkai Palming. I Tenkai all the time. Everyday in a routine you will usually see a tenkai palm here or their. I use it far more than regular palm. The only times I really use regular palm is when I am performing Kaos by Daniel Garcia and card to pocket.