Can't say for sure for the Brussels airspace part, but i'm guessing Brussels gets those descending to FL260 , they have to be FL200 for the HELEN-arrival or FL220 for the DENUT-arrival.
NORKU-arrivals have to be FL280 or below at NORKU, EEL-arrivals have to be FL260 @ the boundary.
Departures to WOODY have to be WOODY FL240 or above, and 5nm north of NIK FL260 or above. BROGY-departures have to be FL250 or above 13nm North of BROGY.
Hope this helps.