There is a flat seating ring on the hull roof of the Tiger, surrounding the turret opening, to which the turret can be bolted. While this ring is invisible in most Tiger models, it becomes very prominent in models such as this because the turret gets lifted out or omitted to display the interior.
Although Rye Field's kits seem to be the basis for Ustar's new model, Ustar have not repeated the errors in Rye Field's seating ring. Instead they made a new design that seems accurate to the real Tiger. This photo shows Ustar's turret roof and part of their seating ring. It has four problems.
Firstly, the ring has two unwanted depressions in it. This is one of them. They are probably related to Ustar's plastic molding technology. They should be removed.
The second problem is the omission of the hole (here) for the turret lock.
This is the real hole. It would normally be filled by a retractable post, but nevertheless should be very visible. Note also that Ustar have slightly misplaced two of the holes in the ring.
The third problem is that Ustar's ring is not lined up exactly with the hull roof. At the top of this image we can see the roof's central weld line, which is correctly placed. Below it you can see the bolt holes molded into the seating ring. They should be symmetric around the center line, but Ustar have rotated their entire ring by about 1 degree.
And fourthly, we get the wrong version of ring. This diagram shows the turret ring for the Tiger version that Ustar give us. They have used a seating ring with more bolt holes than you see here. It's correct for later versions of the Tiger but not for the kit. You can correct Ustar's ring by filling all bolt holes that are not on this diagram.