Besides setting the convergence, you can play with the gunsight inside the cockpit.
There are 2 controls:
[ul]
[li]Sight distance (from 150 to 600 yards)
[/li][li]“Adjust Sight” (from 30 to 100 feet)
[/li][/ul]
The effect of both controls seems to be the same: increase / decrease the separation between the 2 horizontal lines.
Im a little confused. How to use these? Why mix yards and feet?
Anyone?
http://www.combatsim.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic&f=52&t=000164
http://forum.axishistory.com/viewtopic.php?f=114&t=17850
The lens had a numerical aperture of F/O = .68 through which a large circular graticule was projected onto a circular glass reflector screen 3 inches in diameter. The graticule was bisected by a cross, the horizontal bar of which was broken in the centre, the gap being set by (1) a knurled ring which turned a perspex pointer to various range settings, and (2) an adjustable ring which turned an indicator to wingspan in feet. The internal mechanism then set the gap according to the required range. A central dot provided a further aiming point. We set the span dial to the known wingspan of the e/a, and the range dial to the max.for accurate fire.
When the target coincided with the gap it was within range. The radius of the graticule ring gave the deflection allowance for hitting a target crossing at 100 m p h.
Much clearer now 
Sporran, Im afraid the the Hurri/Spit gunsight will only allow you a min. distance of 150 yards, but you can set convergence to 100m (around 110 yards)
The sight difference between 100 and 200 yards can be ignored. The difference in bullet drop will be less then 10cm between those distances.
If you set your sights to 300m (~330y), you will shoot around 20cm high at both 100 and 200m, then again the sight offset from the bore line is much higher in a fighter then in a rifle, and that might actually be an advantage.
Would need to test the setup on a range on paper. Anyone have a Spit of Hurri they could loan me for some tests? 
I think that “adjust sight” is the setting about the wingspan of the target
es:
Bf 109 wingspan 9.925 m (32 ft 6 in)
He 111 wingspan 22.60 m (74 ft 2 in)
Me 323 wingspan 55.2 m (181 ft 0 in)
Exactly Pesca.
So I think that the actions to take are:
1.- Before flight: Set convergence
2.- In Cockpit: set Sight Distance to that of convergence (or maybe a little more?)
3.- Before engaging: set target wingspan.