If you are in F or can see the seat map in F, this could help: 13 seats in F=large screen, 17 seats in F=small screen, 14 seats in F=a bit of a lottery.

777s with small screens: All G-ZZZx (A/B/C); G-RAES; G-VIIx (A-N and S).

777s with larger screens: All G-YMMx (A to P); G-VIIx (O,P,R,T-Y).

The G-YMMx are the extended range (ER) 777s with the larger screens and 13 F seats (14 minus one for a crew rest).
The G-ZZZx are the shorter-range "A-market" 777s with the smaller screens and an extra row in F (17 F seats).
The others (G-VIIx and G-RAES) are IGW 777s with 14 F seats, and screens as above.

Thanks to G-BOAC for this (lifted from your earlier post) and others.