Oracle 10g memory allocation

 I am running Oracle 10G. I have 4G SGA managed by automatic memory system. 3G is currently allocated to the Variable Size and 1G to database buffers. The application that uses the DB uses lots of dynamically built SQL without binding variables. I think this is fooling the "Automatic memory system". Its there a way to determine what is the best way to allocate the SGA. Or some report that will tell me if my variable size is too large. Most of it seems to be allocated to the 'shared pool sql area'.