If the cover letter and additional documents are so important, why doesn’t the ICA ask for it?
If the ICA asks for a cover letter, everybody will be sending cover letters that have no real value. The same goes for the additional documents – applicants will just be clamoring to find as much paperwork as they can to support their case. The ICA does not require these things because it will take them a longer time to process everything. However, if you submit a cover letter and additional documents that are well planned out, each one contributing to your unique case, then your application will stand out.