I'm not so much talking about fog patches as low cloud especially over water enroute in a SEP. For example, if you were flying from the UK to say Holland and you knew there was a narrow warm front over the sea but it was clear in the UK and clear in Holland. Would you undertake the flight where you intended to fly at 6,000 feet above a 4,000 layer of stratus which went down to 500 feet amsl over the sea. If not, what base would you accept. I'm just curious to get peoples views as risk acceptability varies from one person to another.