Ok playing the devils advocate....
I checked my 109 props, with J-cats 109s in and running. I think the propeller is just fine as is.
Keep in mind, that the POV of the camera in the vid. is significantly removed from that of the pilot. Its high, rear mounted location restricts its actual "forward view" THROUGH the front panel to a very acute degree, and allows you to see the prop above the upper bar. This gives the illusion of a massive propeller arc.
The pilots own POV however, is much closer to the front panel and at a lower level, affording a significantly greater angle of view beneath the top bar of the front screen. Also, while you are correct that the closer we move to an object the larger it APPEARS to be, in this case, with the propellor some 2-2.5 meters away from that upper bar, as you move forward in the cockpit, the angle you could "see" would increase faster than the rate at which the propeller diameter APPEARS to grow. The prop arc should fall on or just below that front bar from his POV, as it does in J-Cats 109s in game now.
Also, as the planes in IL-2 are proportional in size, and (for the most part) use historical size and scale data, It would make sense that what would need to change if anything would be the players POV. not a change to the model of the 109.
Just saying, let the barrage begin..