Welcome to the forum.

But what you didn't say was what sight picture you were starting with. The Sigma sights are made to cover the bull, not lollipop like most of us were taught. That can obviously lead to low shots.
As far as shooting left, that's somewhat of a normal comment about the Sigmas. Mostly it's a matter of dealing with the long/hard trigger.
And then the final factor is the bullets you're shooting. My 40 shoots lower with lighter rounds.

__________________
Pete.