A few suggestions.
More volume means more weight. And the farther forward that the center of gravity of a large bag is can increase handling impairment. So, more volume is great, until it isn't.
My largest bag is roughly 9.5 liters in the photo below, this is the bag I use for touring. This photo is repeated from the link that I included in a previous post above.
Note how close the part of the handlebar bag bracket that would normally attach to the handlebar is to the steerer tube, it is only 55mm. The center of gravity of my bag is as far back as I can get it. When I put my bag onto the bike, I immediately notice the change in handling, and at slower speeds I notice the front wanting to flop over to one side when I make a tight slow turn. I want my bag center of gravity to be as close to my steerer tube (steering axis) as possible so the handling is impaired less.
I mentioned that for randonneuring, I use a smaller bag and that is why I use a smaller bag for that purpose, less volume means I can't put as much weight in it and the handling is impaired less. That forces me to use my saddle bag for somethings that otherwise I would be tempted to toss in the bag that is in front of me with easy access.
Quite frankly, I would not want a bag any taller than mine, as all the stuff in the bottom would get lost. I find it takes some work to keep it organized on a tour, I put a small cardboard box inside it to help me keep most things oriented vertically, like tooth brush, toothpaste, chain lube bottle, sunscreen, repellant bottle, partial roll of TP, phone, power bank, granola bars, sunglasses case, etc. (The banana sits on top of everything else until it magically disappears.)
And one other thing that is not readily apparent when you look at that photo, the most dense (heavy for the volume) stuff like my powerbank is to the rear in the bag and least dense stuff like sunglasses case is forward in the bag, that is an attempt to shift the center of gravity further back towards the steering axis to reduce how much the handling is impaired from the extra weight.
The bag above has been out of production for over a decade, and I made some modifications to it. So, I can't recommend you get one like mine, you won't find one. But I am pretty happy with how well it has held up over the years, but it clearly is getting worn out.