I was messing around with this with the PC98 font, and I think there might be an error with how it handles widening the fonts compared to the hardware. It seems to work just fine with kana, but when it comes to kanji, it doesn't seem to want to recognize anything. I took a closer look and I think I'm starting to see why.
Here is an example from Legend of Heroes 3:
and here is the output for the kanji 大 from fb.exe with text_xmax set to 1:
If you look at the Legend of Heroes 3 image, you'll see that there's a bit more open space up in the center of the kanji. In fact, I've noticed that in any case where widening the font makes it overlap with another pixel, there is a blank pixel on the system, rather than a filled one.
Same thing with the kanji 祝:
It might be easier to see with this one. You can see in the LoH3 shot how the top right of the 礻has a clear pixel as it touches the 兄, but in the generated character image, it's all squashed together.
The result is that the program can't find the characters since they don't match. I'm not sure if there's anything you can do about this, or if I even correctly identified the issue, but I thought I'd mention it either way. And yes, I did generate the TTF font myself from the same system that this screenshot is taken from.