I know I'm going to regret this, but like an accident on the other side of the highway, I can't help but look...……….
The grey Mark IV is the exact same tank as the white Mark IV; the grey Mark IV I have on hand measures 55mm from the bottom of the metal track to the top of the deck of the tank.
So, no deception here on the part of War Park; their tanks and figures are advertised as 1/30th, the tank is in fact 1/30th according to your specifications.
The ruler I used to measure has not be certified as accurate, I am not sure if it is properly calibrated, it's wooden and I've owned if for over 50 years, perhaps shrinkage has happened over time, much like what happens with a dip in the pool when the water is cold.
I don't have any GD figures handy at the moment, but again, War Park is advertised as 1/30th, their Kharkov figures are all 1/30th, numerous pictures are available on the internet showing War Park figures side by side with other 1/30th scale figures and they match up well.
In the photograph you claim shows "The heads of the GD figures are WAY below the tank deck"; again, look at the angle the photo is taken from, it's not ground level, it's looking down on the figures and the tank.
That's all I've got.
You're welcome.