I am thinking that being close to WHERE the vitals should be will be more important than being close to the SIZE of the vitals.
We as a group (hunters) have been taught where to shoot over the ages and I believe that this information is a bit faulty.
Read the thread above about aiming locations. Look at those pictures. Change your thoughts about where the 'shoulder is when people say "shoot behind the shouder".
Make your kill zone off shape (see Terry's thread), not round or square.
Go into the International Bowhunter Education Foundation site and see if they still have the training exhibits that include cut outs of the deers heart, lungs and liver. Take those shapes and incorporate them into your "entertainment".
Good luck and make it fun.
ChuckC