B737-300/400 Bug setting

[lowandfast]

I'm flying both 300s and 400s. I was reading in my revised FCOM that on landing now we have to set outer bug at Vref+15 on the 300 and Vref+20 on the 400. Previously the bug setting was simply Vref+15 both for the 300 and the 400.

Is this change related to the engine failure on final procedure where we call for G/A thrust, flaps 15 and aim for Vref+15 on the 300 and Vref+15+ additional 5 knots for tail clearence during flare on the 400?

[Centaurus]

Vref+15+ additional 5 knots for tail clearence during flare on the 400?

Searched the FCTM but unable to find reference to extra speed for tail clearance? Someone's personal opinion, maybe? What is a grey area is the Boeing policy of further adding the HW component and gust factors or minimum of five knots on top of Vref. Is that applicable to engine failure on final approach where you select Flap 15 and continue at Vref30/50 plus 15 knots min.

[Empty Cruise]

Has always been +15 for the short'uns and +20 for the long'uns

[soundlover]

I knew that the Vref+15 knots was to indicate at what speed you should limit your bank angle to 15°, maybe Vref+20 is something similar...