Too small? Are you referring to the packs volume, or its torso length?
Two torso lengths - short back and long back.
The long back is longer and thinner, only by a few inches
zip up the sides (with the side pockets off), the main sack reduces to perhaps 70lt size.
The short back is shorter and fatter, only by a few inches)
zip up the sides (with the side pockets off), the main sack reduces to perhaps 40lt size.
100lt zips open
120lt with side pockets attached
(10 lt each side pocket)
It weighs 4kg empty!
Taking into account that the concept of these bergens was for the bottom of the pack & therefore the load to be supported by the soldiers webbing, hence the comments about webbing worn or not worn and the designs minimal waist strap. So for torso length I made the following notes from other post including the ARRSE forum:
5' 7'' short back ends near the bottom of the ribcage
5' 7'' long back works as a normal trekking rucksackwhen worn without webbing
5’ 11” long back works as a normal trekking rucksack when worn without webbing
[I'm 5’ 11” & the long back fits perfectly as a normal trekking rucksack, but IMHO the waist strap is too narrow]
6’ 0” short back version is the right length for use with webbing
6’ 0” long back works as a normal trekking rucksack worn without webbing
6’ 0” plus, the long back version is the right length if you are using webbing
HTH