As for measurements, I concur "fl" sounds like some aspect(s) of the hull in the water - what I would have called the "wetted hull" - so maybe "fl" stands for fluid- or flow-something. This would be logical for hydrodynamic engineering, as it would figure largely into a ship's cruise/power characteristics, whether located at the waterline or (anywhere) below it.
The standard types of measurement are "WL" - meaning strictly at the waterline - and "OA", meaning over-all - which includes not just the hull but the entirety of the vessel such that, on a carrier for example, it includes the flight-deck overhangs. On your Mogamis note, the beam OA would also include the deck-edge gun tubs. (Really, WL measurements are commonly the more useful of the two.)
In any case, I can certainly believe your finding that the Bandai CAs are too beamy - even for Mogamis. And that, for building they are no doubt far less attractive than the 500-scale Nichimos. (I may resurrect my earlier thread on exactly that.)
But what I really want to see is your analysis of the Bandai battleships - particularly the Yamashiro mold - as that is "the only game in town" for this unique (Fuso-) class, in this scale.
So, THANKS Billy and send me your BB pics, with your writeup on those, when ready, sir!