The software is very simple to use so there is not really a question of using it properly.
Just make sure that any filters eg military, helicopters etc are cleared so that all flights show.
Only the planes that are actively 'squawking' on ADSB are tracked.
The system works by the plane transmitting ID & other data periodically.
This data is collected by ground stations & uploaded to the tracking sites.
If the planes are not transmitting or the ground stations are not uploading then the planes will not show up on the trackers.
In my experience the thick persistent trails usually occor at altitudes below that at which a 'normal' trail would form.
Generally contrails normally occur at heights around 30000ft give or take a few thouand feet according to daily atmospheric conditions.
This is the normal cruising altitude for airliners, at that height it is very difficult to see a plane with the naked eye yet alone pick out details of the plane.
A normal contrail needs three things, humidity, atmospheric pressure change, and sub-zero temperature to form ice crystals and only at heights around 30000ft are these three thing reliably consistent.
Not sure what you meen by 'very steep flight paths' because at the altitudes the trails are seen at the planes will be flying straight and level.