Originally Posted by
cleong
I think it’s so that the shape of the rear hull can remain accurate, otherwise the gearbox frame would have to be in line with the sprocket to provide drive.
Tamiya need not use gear ratios to tune the tank’s speed as it is possible to tune that using the MFU programming - for example, in Tamiya 3 speed truck gearbox MFUs, the maximum current in each of the three gear positions differs.
That's a Mk.13, it had that part of the hull extended so they could fit in an additional fuel tank. The feature your pointing out would be even more pronounced on earlier hull types. Interestingly the Israelis made the same modification to their Mk.3's and 5's when they upgraded them with the L7 cannons making them into Sho't Meteors.