Jack,
Did some measuring of current Axis & Allies tank sizes. No matter the real-world relationship between tank size, the current convention is to stick to a given range, and depending on a tank’s relative size put it either at the top of the range (Panther) or bottom of the range (Type 95), etc.
Here are the measurements: (Length is point to point on longest part of tank / Width is track width)
UK Matilda
20mm L / 9mm W
US Sherman
22mm L / 8mm W
GER Panther
22mm L / 9.5mm W
RUS T-34
21.5mm L / 9.5mm W
JAP T95
19.5mm L / 8.5mm W
ITA M41
20mm L / 9.5mm W
Obviously the Panther is the largest (and widest) tank, and the T-95 is the smallest. Here are my proposed measurements for the French lineup:
Hotchkiss H35
17mm L / 7.5mm W
SOMUA S35
19.5mm / 8.5mm W
Char B1-bis
21.5mm L / 9.5mm W
There is an orderly progression from light to heavy tank, taking into consideration that even the Char B1-bis should be smaller than late war tanks like the Panther. The Hotchkiss is a tad smaller than the current smallest tank, as befits a very early war light tank. Jack, do you like these measurements? The SOMUA and the Char B1 are close in size, but they are very different tanks in appearance and it should be no problem to tell them apart.