What possessed me to spot dodge with Marth just sitting outside my FTilt range?
you spotdodge in spots that are useful
you spotdodge when attempting to avoid marth in his effective zone (e.g. sh fair, sh nair, dash db) or when you are performing a 2nd level read on his bait (e.g. instead of FF fairing on your block he just opts to "tomahawk"/land)
marth recognizes the situation and just walks into that range