No, the Vf is always measured the same way: ~5cm long 20AWG teflon wires were soldered to the ledboard, the the wires for voltage measurment are clipped at the end of those wires. Ideally you want to solder separate voltage wires right next to the led but I never do that. The voltage drop over those wires is small but not negligable: at 5A it is about 0.03V, this should ideally be substracted from the voltage value.