However, in no event shall the share of the net profits of any trade or business in which capital is a material income-producing factor be reduced below the amount which would, without regard to the provisions of this subdivision, be treated as the earned income derived from such trade or business under section 911(b). In making the computation required by this subdivision, any trade or business with respect to which the individual renders substantial personal services shall be taken into account irrespective of whether a qualified plan has been established by such trade or business.
26 C.F.R. §1.401-10