The AA% doesn't matter as much as what it tastes like.
The stats may fit but that doesn't mean the flavors fit. When you say 'Belgian Brown, I think of a brown porter-esque grain bill (coffee, chocolate) as opposed to a traditional BDS recipe (burnt sugar, figs, raisins).
If it doesn't fit in 18E, just go with what it does taste like. If it tastes like a 'Belgian Brown', 16E or 34B (Mixed Style Beer) as we transition to the 2015 Guidelines.
You're saying that the beer is brown but the malt character isn't noticeable? Can you share your recipe? Unless you just used a little bit of roast malt to change the color, there should be some malty flavors in there somewhere.
I like to condition my Belgian ales because I do think they change over time. The 'rough edges' soften, the malt and yeast flavors become more integrated, and clarity improves.
You won't get more malt flavor with age, but you might get a higher perception of flavor as the edges soften and particles settle out. Conditioning time depends on several factors, but a few months wouldn't be unreasonable.