The Soviet ergonomic standards guide requires a standing loader to have 1750-1800 mm of standing space. The height allotted by the ST-I is only 1680 mm, but 1750 mm standing room is a pipe dream: out of all WWII era tanks listed in the guide, only the Churchill comes close with 1700 mm. 1680 mm is superior to all other vehicles in the table. The breech axis is a little high, at 1130 mm, but the gun does not have a horizontally sliding breech like the manual suggests it should for a height of 950-1000 mm or more.
The data for the gunner's seat is not given, but the proportions of the loader's position allow us to overlay the ideal gunner position over the drawing.
Looks like an almost perfect match, with the sight being a tad too high. Unlike his loader friend, the gunner would have found this tank comfortable to use.
Via Yuri Pasholok.