;-)
There will be a formula that could be created to calculate how much ammonia your stock would produce, though there are so many vairables involved no 'simplified' version is available...
Bacteria can and does live on surfaces throughout the system. So the more surface area you have in the system, the less bio media you will "need"...
In my experience, in every tank I've ever kept, absoultely no bio media is "needed". So my advice is any bio media you offer is "extra". This is not to detour you from using bio media, but instead to help you best guage what you "need".
Therefore I don't think you shuold consider any bio chamber "to small"...
There are also methods to better utilize a bio chamber. Using the "wet/dry" approach as opposed to submerged bio media will provide additional oxygen to the bacteria which in theory will allow a larger or healthier colony to exist.