Where you are, I wouldn’t think any other than the stock antenna would be necessary. Is the antenna on the correct band?
Are you using Sentinel to program the scanner and are you programming your own Favorites List? First, I wouldn’t use the database for the most part unless you are traveling. Create your own Favorites List, if you haven’t. If you want to use the database, you have an extremely large range (50 miles) selected. It will take a long time for the scanner to travel through the list. And there will be a lot of frequencies and trunked systems in there that you won’t hear, further wasting the time of the scanner. I would shorten it to zero or five. You will still hear more than you are probably looking for.
If you need a helpful website to sentinel, here is one:
BCDX36HP Sentinel Software Manual
There is also a Mark’s Scanner page for the 436 and 536 that is helpful.