Mr Evil said:
... a good size for a male is around 6ft although some call 5'10" so we shall just sit at a simple 180cm = a smidge under 5'11"
the scale has been called at 1:65 = 1800mm divided by 65 = 27.69 rounded up to 28mm
now the vehicles i have are 1:64 = 1800mm divided by 64 = 28.125 rounded down to 28mm.
All that is fine (and I'm not trying to be a scale thug here) but I believe the soldiers are NOT 28mm. I'd love for someone with an actual figure to post it's actual height! They are probably 28mm to eye-level. And that's okay, but since vehicles don't have an "eye-level" and only absolute dimensions, it means the soldiers are not "on-scale" with the vehicles.
The M1A1 Abrams is 144" wide, or exactly 12 feet. At 1/65 scale, that puts the vehicle at 56.27mm wide. And I'd wager big money the vehicle is spot on to those dimensions within a hair.
Now take a soldier and measure him to where you think his head is. Call him 6' tall if that makes you happy At 1/65 our intrepid soldier should come in (as you said) right around 28mm (give or take .25 of a mm).
But at 28mm to eye level, and 31-32 to top of head, our soldier is no longer 6' tall (well above the average human today) and more like 6'10" tall. At 1/65 every mm is worth about 2.56" in real life.
I think those infantry figures in your last shot look great next to that vehicle, and spot-on compared to that real-life photo. I look at the fig and the door on the vehicle and it looks like he "could" open the door and sit inside. But those figs are likely smaller than the BFE infantry figs.
And the SST trooper looks way, way to large to fit into that vehicle. I know the BFE are supposed to be smaller than SST so here's hoping they look right when up-close. Like I said, not trying to be a scale snob here, I really don't care WHAT the scale differences are, as long as they look good next to one another.
Steve