The Tiger's turret wall was a single sheet of steel, bent into a U-shape. Under the "chin" of the turret was a curved metal bar to fill the gap.
Here is the "chin" of an Early Tiger. The weld at (A) joins the curved bar to the wall. Notice that the end of the bar is machined flat and it blends in exactly with the wall.
Border's Early Tiger turret has an obvious flaw here. The end of the bar, the area (A), does not blend in with the wall. There is a significant recess. The other side of Border's turret has the same problem.
You can add a piece of modeller's plastic card to bring that area into line with the surrounding wall. Then, when you are sanding it down, you can create the gentie curve at (B) in the first photo.
This is the other side of Tiger "131". The curved corner marked (A) is a deliberate design feature of the Early Tiger.
There is another problem with Border's turret. They apparently have problems aligning the parts of its mold. This results in vertical seams, like (A) here, and steps like (B) that you should erase.
Looking at the underside, we can the result of the mold misalignment. I have pointed out a slab of plastic that protrudes. The real turret, remember, had a smooth continuous curve along here.