When setting up your client's income, the system will allow you to choose either "pro rata" or "asset specific" and will act on your instructions to generate income. Even if you hold sufficient cash for income, if you select "pro rata" the system will sell down across the client's assets pro rata to generate the income. If you want to ensure the system targets cash in Product Cash for income, then ensure you select "Asset Specific" when setting up the income, then choose 100% Cash.