RE: the rational of trimming
Do not compare efficiencies with area!
The large fuse adds lift but not an equal amount (area to area) - nor should you likely want that -
IF efficiency were equal -things would get touchy
If you have ever made a large flat (profile fuselage) you would have noted the model does not turn as it a rolls -it simply assumes a different attitude. very strange.
However properly setup it can work to an advantage.