Scanning only in middle of the screen

Hello,

I'm using your plugin in order to scan article in a warehouse. 
It's working but i want to know if it's possible to only scan when the barcode is in the middle of the screen ?

When i've 2 barcodes on the screen, the plugin focus everytime the barcode on the bottom.

I thought the drawsight options was used to allow you to only focus on middle but not?

Thank you