Where a retail salesperson ordinarily paid solely by cash commission receives remuneration in a medium other than cash, the employer need not withhold on it if it files the information the regulations prescribe. For tips that are wages, withholding applies only to tips the employee has reported in the written statement section 6053(a) requires, and only so far as the employer can collect the tax, at or after the statement and before the end of the calendar year, from the wages under its control (excluding tips but including funds the employee turns over for the purpose); the regulations let the employer collect over the quarter and allocate shortfalls across income and FICA tax.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.