How can you create a custom keyboard layout in fingerterm with more than 11 columns?

[arachnist]

I'm trying to define a custom keyboard layout for fingerterm utilizing 16 columns instead of the default 11, and i've hit an obstacle - only 12 keys (well, actually, 10 full ones and 2 halves) are displayed.

Is there a way to define a key width, or make fingerterm automatically calculate it, based on the number of keys in a row?
Judging by the code it should already handle that case, but - apparently - it doesn't.

Here is the keyboard layout i'm trying to use.