Your observation is correct,
normally fog is present with no wind, or as much 1 to 3 knots, cause by condensation of humidity by a saturated mass of air, when the temperature and the dew point are near to similar or the same, and it is off when the sun rise, and has no too much height.
You can have a very clear and springy day over it at may be 200/500 feet above land, except if you have stratus in contact with land, then its height is much more.
The SH3 "fog" is more... a reduced visibility caused by dense rain.
Sadly it is what we have, and what we must to enjoy.... may be in SH5 :p