328i sedan, 6MT: 3340 lbs, 50.5% front, 49.5% rear.
328i wagon, 6MT: 3527 lbs, 53.8% front, 46.2% rear.

(Stats from bmwusa.com)

The wagon is heavier than the sedan. That makes sense. But why would the wagon be MORE nose-heavy than the sedan? Shouldn't the extra weight of the wagon (presumably in the wagon area, which is the only difference I see between the cars) make the wagon LESS nose-heavy? What am I missing here?

isn't the coupe heavier than the sedan? i thought it was supposed to be viceversa.

BMW likes to place a lot of things under the rear seat. Perhaps, this was not seen fit in a wagon... thus, components moved somewhere else up front?

Do they relocate the battery to the front for the wagons? I know that the battery wouldn’t weigh enough to generate that significant difference, but it could be a cause.

probably to balance things off after you've put in your dog/ grandmother's wheelchair/ brand new jagermeister machine, etc, etc, etc......

Is the chassis/wheelbase the same on both cars? Because I van imagine that the if the wheelbase was longer on the wagon it could make sense. The wagon has mostly air on the rear end, while the front while the front end has to 'carry' the engine etc.

If the wheelbase is the same all the above is non sense and has to be ignored

Sedan: 108.7" wheelbase, 178.2" total length.
Wagon: 108.7" wheelbase, 178.2" total length.

Good theory though.