After assembling the upper and lower hull, I compared the UM Hetzer with my built up Fujimi Hetzer. I'd have to say that by eye, they are very similar in size, though the barrel of the Fujimi Hetzer is much thicker.
The UM Hetzer is much wider, but with the way the armored skirts of the Fujimi Hetzer stick out, the difference in width is not so apparent to the casual observer.
Now that I am looking at the photo of the Bulgarian Hetzer again, I also realize that I used the wrong type of rear idler and headlight. The color profile that I was working from got these wrong. The UM kit actually provides an idler like the one in the photo, but I'm not going to bother correcting it. Oh, well.