Direct comparisons, yes, but the point still stands - Aventras have a sizeable gap between the rear cab wall and the passenger saloon compared to some previous trains. If you look at electrostars, the cab wall is practically non existent!
However, just in the interest of a more direct comparison in lieu of a technical drawing, here's an
interior and
exterior shot of 710261. By my reckoning, the passenger saloon ends roughly in line with the right hand edge of that silver plate, meaning everywhere between there and the black line next to the cab door is effectively 'dead' space - although it will actually be filled with electrical gubbins of course.