In this scope, there are several possible causes of laser motion with altitude change:
1) focuser plate flex. While certainly possible with a Paracorr and an eyepiece, the angle of change wouldn't be exactly vertical (as it is).
2) Ring flexure. Still unlikely for the same reason as #1.
3) spider flexure. When the scope is vertical, the secondary's weight hangs under the spider. At the horizon, the weight hangs beside the spider and causes twist in the spider vanes. High likelihood of this one because the spider is not in tension. A couple possible cures: thicker vanes (not desirable because of weight and extra diffraction), or a small counterweight outside the spider (no extra diffraction because it's behind and smaller than the secondary holder) on the center bolt. Or, of course, some other way to mount the spider.
4) movement of the secondary center bolt in the spider hole. Try wrapping the bolt in plumbers tape until it fits tight in the center hole. Or, wedge toothpicks in the corners to make it tight in the spider.
5) sag in the poles. The long poles could easily sag when the scope is pointed low, allowing the UTA to move toward the ground. Though this is a light UTA, my impression, by grabbing the UTA and shaking the scope back and forth, is that this scope would have benefited from 1.25" poles. If you change them, though, to that diameter, it will throw off the balance quite a bit.
6) Flexure in the lower attachment brackets of the poles attached to the altitude trunnions or torsional twisting in the trunnions themselves. if I were to quantify this issue, it would be smaller, but it could be an issue since the pressure is very different when the scope is vertical than it is when horizontal.
All of these issues have solutions, but I'd start with #3, 4, 5 first.
Are these problems with all ultra compact scopes? I am considering buying an ultra light structure with a flat ring for the UTA.
There are some European Ultralight designs that would interest me. Also, we need to be careful generalizing about all of these types of telescopes. I've been reluctant to be overly critical in public forums because of my respect for Dave Kriege and Obsession telescopes. He will be looked upon as an innovator and one of those who moved ameratuer astronomy to new heights by offering excellent telescopes at reasonable prices.
The Upper Assembly is simply a Birch ring. Also, there are only three support points for an 18UC vs. four for the 22. That may be why the 22 holds collimation better. A simple check comparing the Obsession UC design with their classical telescopes reveals that the Upper Assembly is much more robust for the Classical than it is for the Ultra Compact.
In my opinion, the 18UC is not one of those telescopes that will be noted for their excellence. Maybe it is not a bad telescope, just not an excellent one that you would expect from Obsession. With my 18 UC, I had more issues than just the fact it would not hold collimation. I am just going to let it go at that for now.
I see that Teeter is coming up with an Ultra Compact/Light design. I see some design features in the Teeter that might play out better with his Lite telescopes.
In my opinion, there is a place for this type of telescope. I would bet that various design modifications will ultimately be made so that they are good performers.
For me, the extra portability of the 18UC did not outweigh or override the performance that an Obsession Classic would have provided. I thought I could just grab the 18UC and throw it in my SUV. I could not. I had to use wheelie bars and ramps. I could have used wheelie bars and ramps for an 18 inch Classic--but received excellent performance across the board.
If someone owns a Honda Accord or Toyota Camry or similar sized vehicle, then yes--you could fit an 18UC in the trunk of your car, something you could not do with an 18 inch Classic. So, yes there is a place for this telescope.
However, if one has a vehicle to haul a Classic, or if one does most of his or her viewing in the back yard, then I believe that person would be better served with the Classic Obsession--a mighty nice telescope.