Remember a while back, GSX DID send only large tankers to the Concorde. If it worked before, it can work again.
The kind of refueler truck was always decided by the standard variable that holds the total fuel capacity of the airplane. Nothing has changed for this condition.
What has changed in "recent" ( not really, it's like this since a couple of years ) versions is that. in addition to the total fuel capacity, there's an additional condition for the large tankers to appear, which is the height of the refueling point under the wing. The larger tanker won't be used if the refueling point is too low. Less than 3.40 meters from ground, as it is now.
So, maybe you'll have to check if the refuel point on the Concorde is configured to be at least 3.4 mt. from ground, which explains why the larger truck is not used.
In any case, we are still not done with the refueler function in GSX. A fuel hydrant is still missing, and we are working exactly on that, right now. This should be able to service more airplanes kinds, not just those with a wing high enough for the truck to end up underneath.