Oh, so you mean I can add a blank tile for space width? How will the converter determine the size then if there is no glyph color? I just tried using a blank tile and adding a space character in the "Glyphs in image" section, but it turned the space into a one pixel wide character, which should help, I just need to use double spaces.
I also just realized that each character already has a 1 pixel space in front of it, adjusted by the "Spacing" option. So my previous comment actually means "I want the spaces in my font to have a width of 2 pixels, but the converter defaults it to 3."
If there are no other options, then it's fine, because at least I can resort to using double spaces which is more manageable than wider spaces.