Here is a good article on grip technique:
http://www.theshootingschool.org/articles/The_Combat_Grip.pdf
I have to strongly disagree that the support hand isn't important. It's critical to controlling the weapon and tracking the sights. I think you'll find the finger on the triggerguard works fine for shooting casually, but as you try to increase your shooting speed and/or work on more defensive shooting you'll find the extra tension will cause the sights to track poorly. There are a few pros that still use that method. Ultimately it's what works for you. I'm still making changes to my grip and experimenting with different things so there really is no right or wrong way. I would look at it more like what works and what doesn't. I think I remember Matt Mink shooting with his finger on the trigger guard.
I didn't say it wasn't important, I simply pointed out your shooting hand is much more important, and modifying the support hand as needed isn't that big of a deal as long as it is comfortable and does the job, support. I also said adjust as needed, or in other words if a grip hurts your shooting, then change it.
I have seen first hand how big of a difference changing the support hand grip to something different than "the norm" can make for many shooters. I have seen unusual grip techniques, specifically with the support hand, allow for much improved shooting... for example, a very petite woman to shoot a .50 cal DE rapid fire with more accuracy than anyone else could at an NRA trainer workshop, and there were several state pistol champs at this event. I have also seen abnormal support hand techniques take very inconsistent shooters and make a world of difference.
Just because something isn't the "norm" doesn't mean it is bad. Accurate, quick shooting has a lot to do with comfort. If you have to keep readjusting your support hand and think about what you are doing because it is unnatural and uncomfortable, it is going to hurt your shooting. If the OP feels better with this grip (and from the sounds of it he does, and is shooting better using it) then there is nothing wrong with it. Consistency is much more vital, comfort is much more vital, good shooting hand technique is much more important, than your support hand gripping the firearm a set way (especially if that set way is uncomfortable, hurts your accuracy, and requires you to over think and over adjust to maintain that grip).