Finially got a chance to see how my new Sigma 40ca performed, it functioned flawlessly no issues whats so ever. However, shooter was low with the the first 10 rounds missing everything at 20'. I thought I used the sights correctly but no dice. I moved the target to about 15' and focused on the front sight only and did much better. What's my problem? The back sights are there for a reason, please advise.