The short answer is that they are intended to work with both .
The first issues ( Tank Crews ) were originally made to go with 1/76 vehicles , which is what UK modellers & gamers generally used. The world goes round, and in recent years 1/72 has become entirely dominant, with the vast majority of vehicles now issued in that scale.
So any more recent figures have been made to match that 1/72nd scale. A year or two back I redesigned all the British Tank Crews, for instance, to make them look better in 1/72nd .I try to make them about 22/23mm tall which works out about 5'7" tall, but the size varies a bit as in real people.
The sets deigned to go in vehicles are deliberately squashed somewhat to help to get them to fit. since trying to get a hard metal bottom into a seat can be very trying !
The first issues ( Tank Crews ) were originally made to go with 1/76 vehicles , which is what UK modellers & gamers generally used. The world goes round, and in recent years 1/72 has become entirely dominant, with the vast majority of vehicles now issued in that scale.
So any more recent figures have been made to match that 1/72nd scale. A year or two back I redesigned all the British Tank Crews, for instance, to make them look better in 1/72nd .I try to make them about 22/23mm tall which works out about 5'7" tall, but the size varies a bit as in real people.
The sets deigned to go in vehicles are deliberately squashed somewhat to help to get them to fit. since trying to get a hard metal bottom into a seat can be very trying !
 Tony Barton's advice on Vehicle size for AB 20mm WWII figures){kind=link}