The Siku is an A5, hence the shorter barrel, same one as the A4 but the wedge armour on the turret front makes it look shorter. Empress is, I believe the A6 model, which actually introduced a new, longer barrelled, 120mm gun.
I don’t have the Siku Leopard but I will attest to the general quality of their kit and they tend to be scale accurate with their larger stuff.