I suggest avoiding blanket statements like assertions that the yellow triangle is ALWAYS based on max unballasted weight. On my 1980 Ventus A, the yellow triangle is required by the flight manual to be at 62 knots based on max allowable weight (with full ballast) at 525 kg / 1157 lbs and landing flaps down, airbrakes retracted. Design rules have undoubtedly changed since then, but the POH is always the final authority.