I have done a little W and B on the A340-600, SA and TG's. The max weights for each cargo positon and hold are lower at the most forward and aft positions, then get higher as you get towards the centre of the aircraft.
I was told this was because of the aircraft structure. Eg: If hold 4 was the only hold used and was up to max weight, you could cause damage to the airframe (if you had a tail scrape) as it is so far away from the centre. So instead of having a max hold weight of say 15000kg, it is 9000kg.
The fwd hold may be lower due to the seating config, but on the two carriers I have worked on I doubt it.
As an aside, I know of an Airbus aircraft that was out of the fwd limit by 120 units and flew 3 sectors before it was picked up. It was picked up during take off on the 4th sector
Hope this all makes sense.