Upvote:5
Break it down and explain it like you have done here. The main thing is to be completely clear and transparent about the funds in your account and where they come from to prevent any doubt. They will read the documentation, and you mentioned getting a letter confirming your payments from your employer, I agree this would only be beneficial to include as it will help to confirm the legitimacy of these funds.
If you choose to deposit the commission money each month, make sure to explain this and highlight those transactions to avoid any accusations of funds parking (this is where you put extra money into your account to make it seem like you have more money, read more about this here).