found that increases in corporate tax were almost entirely born by non-management employees and consumers.
This seems tautological to me. Of course increases in corporate tax are born by non-management employees and consumers. Take Management + Non-management + Customers as a group, then Management represent approximately 0% of this group. Also, Non-management + Customers aren't in a position to change the flow of money through the corporation to shield themselves from changes to taxation.
For the majority of corporations their income comes from consumer spending. In those cases it's always the consumer who pays.