I've noticed that I didn't answer your initial question: I've tried to make it fit at least one character with the Tag Panel on its smallest width. Depending on the Windows DPI settings (text size percentage) it can also hold two numbers, but I've observed that it's getting more narrow the higher the percentage.
My idea was to allow for really tiny fields (e.g., holding only 1 or 0 for COMPILATION) if necessary. If it's really too narrow, field size Smaller or a slightly wider Tag Panel should do the trick.
Here is an overview of the percentages of the new field sizes:
I think these new sizes allow for a wide variety for combinations.