I searched the 'net and found this photo of GIs from the 60th Infantry using a Sherman as cover in Belgium. The photograph was taken on the 9th September 1944 according to the caption and the tank still has the Normandy hedge cutter fitted.
The infantry are standing upright and right by the tank so there is no perspective issue. The lead GI is just shorter than the top of the highest point on the tank hull.
The above photo shows a couple of Warlord Bolt Action plastic British Infantry against a Corgi 1:50 diecast Sherman. In terms of height, the figures are about right - when they are on their stands. Off the stands they would be a couple of mm too short.
In terms of bulk, the 28mm miniatures are too big for the 1:50 tank. Compare the soldier's waists with the Sherman's running wheels in both pics.
The bulk issue really comes out when you place a figure inside a scale vehicle: see two examples below.
Here's a couple of Perry 28mm plastic figures with a 1:50 diecast Jaguar car. In theory they should be dwarfed by the car, except they're not.
Two Warlord Bolt Action 28mm plastic figures with a 1:48 plastic Kubelwagen.
Scale and size in wargaming is not so straightforward as one might think.
Next post I will line up some 28mm models from different manufacturers against each other.