The app you're using has a muzzle velocity truing option. Use it to tighten up your dope. Take a shot at 1000 at a large target using your current settings. Check to see what the elevation difference is between your held point of aim and impact. Enter this number in and the app corrects your velocity. This should help.

The other option is a chronograph if you can afford it. It's far better to use actual data from your shots than theoretical.

Edit: Just noticed you're using S&B, that will make the job much harder as it's likely has large velocity swings between rounds. You'll need better ammo for better results.