the condition of the rubber, the amount of detergent in the mix, the amount of water on the glass, weather conditions...they all play their part.
Also the type of glass too, some of the modern stuff is horrible to squeegee off.
The light also plays a part, if it is at the right height and the right angle, and you are cleaning modern, plate glass, no matter how perfect your technique, the dilution rate of your detergent you will see these ghosting, smoke-like blooms.
No matter how good you are, you are still leaving a miniscule film of detergent on the glass, if the light is just right, and at the right angle you can see it.
If you can see it in all types of light conditions you are doing something wrong!
Too much detergent and worn rubbers will certainly cause that to happen.
as for technique;
Staying just shy of the top edge and sides is fine on repeat cleans, but on dirty glass you really need to wash right to the edges.
But a tip to save on detailing at the end is to pre-detail with your damp scrim (as against using your dry or polishing scrim to do it).
And of course a 'dog eared' squeegee blade helps no end too
Ian