I agree that 18 yards is, kind 'a, far to learn how to shoot a pistol; but look at it this way: In the old days we did everything at 25 yards!*
It has been obvious to me, all along, that this isn't an, 'eye dominance' issue. (Where did that come from?) It's, equally, obvious to me that:
YOU'RE NOT WATCHING THE VERY TOP OF YOUR FRONT SIGHT. (Are you!)
Neither do you have your Glock trigger stroking/breaking technique, 'down pat' yet. (Which is the reason, 'Why' I, so tersely, told you to simply read the comments on using the, 'Reverse Chapman' technique that I wrote about in the Pistolcraft Section of my on-site blog.) If you get the added tension out of the upper tendons in your gun-side forearm, you should, rather quickly, notice an improvement over what's happening, now, with all of that predominantly low-left shot dispersion. If it's an encouragement: You show some good raw talent, there - Talent that I'm sure a competent pistol instructor would be able to help you bring out and develop.
Except at my childhood indoor basement shooting range where we were only able to fire up to a mere 12 yards' distance. (Perhaps an ideal distance at which to learn and become proficient with a pistol. 'Why'? Because bad guys usually want to get in a lot closer than this before they feel confident and comfortable enough to effectively threaten you with a pistol.)