Scan height can be changed per part by changing the component height. Usually, this is not necessary, but if you need to, you can do it that way, as shooting height(scan height) is calculated with this value and you can trick the machine to go lower/higher.
I think you should try to find the dust that reflects the light and affects the recognition, adding electrical tape is ok, but this is just a coverup, not removing the root cause. Since you cleaned the lenses, I believe it's on the walls surrounding the camera, which are 3D printed and it's rough surface can catch some dust. Happened to me before and I was able to remove it with tweezers.
From what I experienced, red cross being outside of camera center does not affect anything. I'll test some more and let you know.
Instead of DCAM in tools, I mostly use edit/material/pick test to check the dimensions and recognition of components, it will also use the speed settings, so your components don't fly away because of fast movements.
The recognition window always shows the width/length measurements, so you can adjust them accordingly. However, after the recognition, window is cleared, so use the phone camera to see, how the recogniton looked like. After some time, you'll get a filling, what settings are good.
I should mention, that for laser recognition, scanning height is very important for ICs and small electrolitics i.e. For ICs set it to TOP=0.2, so laser doesn't hit the pins and for electrolytics, set it to Bottom=0.2, so laser hits the black plastic part as top is round and laser cannot figure out the rotation, only the center. Max size of components for laser is around 10 mm, it will be less, if component is not picked in center.