The guy, on the right with his visor open, is wearing an armet with the mail attached to the lower edge.
This necessitates that the mail be in two pieces, one attached to the right cheek piece and one to the left.
I would assume that the mail bevor on the second guy must have a split going up higher than the buckle, else why have the buckle. The would allow the mail to open enough to fit his head through the narrow neck portion. The buckle the should hold this split closed with some overlap.
The guy with the bar grill is interesting.
We can't see exactly what type of helm he is wearing, how does it open?
If the mail attaches to the bottom edge of the helm, I think it does, then this mail must also be in two sections like on the armet. Although not necessarily in center front and back like the armet.