That seems low. I "lose" a little to trub, but definitely not a gallon. I probably bottle 4.75 gallons or thereabouts.
Some yeast strains will compact more quickly and better than others, especially if chilled, so it can really help to use a flocculant yeast strain (like nottingham or other English yeast strains) and either cold crash or let it sit a bit to firm up the trub layer before racking.
I've been winemaking and brewing for a long time, so I'm pretty proficient with racking and I think that helps too. Practice makes perfect, they say.
Moving the vessel the night before you rack also helps, as it allows the sediment to resettle to the bottom, and then not moving the fermenter at all once it's moved keeps most of the stuff at the bottom.
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