After over 4 years of TiR experience:
Seems obvious, but, the Pro-Clip arm does have to be in the correct orientation for it to properly work, which is having the longest arm on the bottom. I've always used it with the most success on the left side of my head, right side never worked well.
#2 The camera should be centered on the Clip not on your head, which is over to the left side a fair bit. Using a 22" LCD, the camera is basically 0.5 - 1 inch from the left corner of the display if clipped on the top of the monitor.
#3 Use the software to get the alignment of the dots pretty well centered in the camera's FOV.
#4 check head movement against camera dot tracking and look for places where 2 dots merge or come very close to each other. When this happens, the camera has a tendency to lose accurate tracking. - The camera may need to be raised or lowered accordingly to allow for proper angle tracking when moving your head around.
#5 Dot tracking size and light filtering settings should be set accordingly. I've always had the best performance from the smallest dots possible and adjusting the dot tracking size lower to accommodate. It basically means the dots stay separate from each other more when certain angles bring them close to each other. - Setting light filtering lower to make the dots smaller will also help cut down on unwanted IR noise in the background of the camera's FOV, which can wreak havoc on tracking.
#6 Just as vertical and horizontal centering matters, so does the distance from the clip to the camera, you may benefit from the camera being a bit closer or further away from your head based on tracking tests. Easy to test, just put your head further or closer when using dot tracking view looking for "binding" where multiple dots merge together and the camera loses track.
#7 The motion allowed in the cockpit has a couple weird limits. For instance, if I look down and zoom in at a part of the lower center dash, and then return to HUD, it may be a bit off, but if I zoom out, by pulling away before I sit back up to look at HUD, it centers properly, almost as if without doing that, the camera in the sim is colliding with an invisible "shelf" that wont allow the camera to retract to original position.
#8 I do reset my TiR centering often. But it's not always necessary for me to do it, I do it mostly from habit. And since i'll lean off to the side to blow a smoke out the window fan quick on auto-pilot navigating to/from airfield. When repositioning myself back to normal placement, re-centering isn't always necessary, but restores the precise alignment.
#9 The more you use it, and fully experiment with the settings and configuration of your TiR setup, the better it will get, and be more natural.
#10 Using TiR really shows you how much your head moves around without you noticing it. Takes some discipline to keep your head centered and aligned unless you want to look around.
#11 Check the sim's G-Force settings as well, it will pull your head cam around without you moving TiR and it will affect your view.
I initially started out with a dead zone in the middle so it would re-lock to center, and gradually over time, my preferred curves became more aggressive and the center dead zone was eliminated. Now, I run a completely FLAT response line on every axis, with increased sensitivity on zoom, reduced on roll and x, y, pitch and yaw all the same.
At this point, I can accurately track planes, missiles, and ground targets visually using TiR looking out of the canopy while jinking, or the other aircraft conducting aggressive maneuvers, or both at the same time. If you spend the time to really experiment and get it properly setup for your environment, it becomes more than an immersion booster, it is a real weapon.
Hope any of that can help.
-EDIT:
After re-reading your post, I do have to say that the vector clip is fast, accurate and fully capable of the same results that the Pro-Clip can get. That being said, I'm pretty sure you have a distance issue. The only reason the Pro-Clip would track more accurately than the vector clip is if it were too far away from the camera.
-Seil