Mutt, where does the minimum ‘conversion’ of 1.15 come from? You appear to have used it as a means of determining the actual wet landing distance, although you note that the book value is larger - possibly because they are not related by a simple conversion.
My understanding (as above) is that for operational certification, a ‘field length factor’ is applied to actual distance to provide an additional level of safety - the required landing distance. An additional distance equal to 15% (1.15) of the factored dry distance should be added when operating on wet runways. This is a minimum distance for operational certification, but operators may increase this according to circumstance. Have I misunderstood something here?
Applying multipliers to aircraft landing distances is not the same as adding field length safety factors; the latter are an attempt to maintain a level of safety and not necessarily about where the aircraft will stop, although in practice they may be a good guide.
Were you relating 1.15 to the recent FAA guidance material? I found it confusing; I would appreciate a pilot’s guide to what it means or might mean in relationship to the discussion in this thread.