The gunsight can be adjusted.
Reflector Gunsight Description:
1. The Reflector Gunsight is mounted at the top of the instrument panel.
2. There is a switch to increase the illumination left and slightly behind the sight. The level of illumination can be brightened and dimmed. In the Spitfire there is a smoked glass sliding panel that can be raised to reduce the outside brightness as required. The slider control is to the left of the sight.
3.There are two rings below the sight to set the size of the markings.
3a. The Yards ring should be set to the aircrafts gun convergence.
3b. The Feet ring should be set to the wingspan of the target.

Reflector Gunsight

Illumination Switch and Smoke Screen ring pull
Setting Convergence:
The convergence is set up in the Loadout screen. Select "Plane" / "Loadout" / "Guns"
Select each gun in turn ("Next / "Previous")and edit the Vert and Horiz convergence to your chosen range in METERS. Convert Yards to Meters as required. It is a good idea to save the gun profile.
Use of the Reflector Gunsight:
During startup:
1. Switch Illumination - On
2. Set the Yards Ring - Convergence Range
During combat:
1. Set your Feet ring to the wingspan of your target.
2. Enemy's wingspan fits between the two wingspan marks when at convergence range.

Enemy Aircraft Wingspans:
Bf109 = 32ft
Do17 = 54ft
G50 = 36ft
He111 = 74ft
Ju87 = 45ft
Ju88 = 66ft
Me110 = 53ft
Hope this helps
Gos