@Phoibos ya.... when it comes to interpreting IRS rules they sure seem to leave a lot of "GRAY" between the Black & White of the text from time to time!!
My read/interpretation (I am NOT a CPA or Tax Professional) was that multiple sources of SELF-EMPLOYED income is what they were targeting... so that you didn't leverage a deduction more than once! i.e. they don't want you claiming the deduction three times because you run three different business. This seemed to me the most logical explanation of the reading.
