Highway Code Overtake Photo

I'm sure most cyclists have seen this, it certainly gets quoted a lot for obvious reasons. But how much room is actually being given in that photo? Well I thought I'd measure it (approximately). The width of the Audi shown is around 1733mm. I've tried place the measuring line at the wheel arches. I've had to guestimate as the Audi is not square on in the photo. The second line is measured approximately from the wing mirror to the cyclists elbow.

The measuring line on the Audi is 7.8 cm, the spacing line is 5.8 cm. 1733 x (5.8/7.8) gives around 1300 mm. Which is 4.3 ft

Here's the link to the Highway Code, 159-203

"give motorcyclists, cyclists and horse riders at least as much room as you would when overtaking a car (seeRules 211 to 213 and 214 to 215)."

Which to my mind is as clear as mud, since I don't believe there are any explicit guidelines for how much distance you should give to overtake a motorised vehicle.