Gentlemen, I believe that the losses that are being referred to as being "per meter" should be "per doubling of distance."
I'm not particularly knowledgeable about horns, but I suspect that the 6db number is correct, *on that basis*.
If so, the 100db/W/1m would correspond to 94db/W/2m, and 88db/W/4m, and 86.06db/W/5m, according to my calculations.
Best regards,
-- Al