Configure PS3 Controller

Hi, first of all my congratulations for this emulator!! I love it!!
My question:
I have a little problem to configuration my PS3 Dual Shock controller. The fire button = to button_1 is placed on the left stick button and I want to change is position to another controller button.
I went to the preference and joystick configuration and there was no problem to map other button configuration on the controller, but the fire button is the only one that don't change place, or don't work on other buttons place.
Is there a way to set it up, because is too difficult and unnatural to move and press fire with the same analog PS3 stick. Thank you.