You have two choices for selection of engine fail height on performance class B aircraft. On the day you can use the actual cloudbase (the wording is "at the point of loss of visual reference") and work out the engine out path from there. Alternatively, and more commonly, at the planning stage you use the lowest height that your aircraft can climb away from (usually gear up and locked) from the AFM. When you're talking about heights less than a few hundred feet, you have the same scenario as on an approach, that you may well have runway/ lights visible when you are below the formal cloudbase. Therefore they give you a table (similar to the ones for minmum RVR for landing) detailing the minimum vis for takeoff. This table applies to all performance categories, but since class A aircraft (all jets and turboprops >5700kg/9 seats) are required to cope with an engine failure on the runway at V1, only the first line applies, giving a minimum vis of 200m. (unless, of course your company is approved for Cat II or III ops, when different rules apply).
Hope this helps!
BJJ