This is unlawful. Keep your fog lights just for fog. Low positioned lights tend to glare, esp in rain.
Being flashed is a pain in the eye at all times and a dimmer flash will still be seen because that's how eyes work.
Chances are people who ignore a dimmer flash will also ignore a brighter flash.
Flash lights only from behind and only if you're after someone to move out the way, dual carriageway or motorway for example.
Don't flash to give permission to move into your path, that's the opposite of the message flashing lights are supposed to convey.
Raise a hand to say thanks or nod your head, don't flash.