Scabbard Flaps and Rain Guards

Many 13th and 14th century sword scabbards had triangular flaps at the throat, extensions of the leather that wrapped the wooden core. Why?

If your scabbard has this a flap like this, you can tie a lace around the bottom of the hilt so the flaps are pressed tightly against the hilt, as shown with a modern scabbard reconstruction above. This would greatly reduce the risk of rain flowing over the hilt and down into the scabbard if you were had to wear the scabbard in bad weather.

The lace does not hinder drawing the sword if needed: the flaps slide easily from beneath the lace when the sword is drawn.

Rain leaking into a scabbard was apparently not a trivial issue, since we have considerable evidence for another independent solution to this problem: rain guards or chappes attached to the sword rather than the scabbard. These rain guards could be made of metal or leather.

Scabbard flaps have survived on medieval scabbards, and are frequently shown on effigies and brasses. I know of no evidence for a lace used to tie down the flaps, but if the lace was only used when the owner intended to ride out into bad weather, the lack of iconographic evidence is unsurprising.

I believe the scabbard flaps were supposed to serve a useful function. My current theory is that in bad weather they could be tied down with a lace to reduce the risk of rain leaking into the scabbard. I think that's pretty plausible, and I don't have a better explanation.