Sorry, I didn't see a folder with the ETO_Spitfire Mk Vb name, and when I checked in game I didn't find it because it is listed as Canadian, and I was looking in the list for Britain.
<Effect Type="Track" EffectName="US_AAF_N6a_gunsight" PosX="0.00" PosZ="-1.25" PosY="0.575" Pitch="90" MinVel="-999999" MaxVel="999999"/>
With this gunsight you can select from three reticle sizes (fighter, bomber, heavy bomber) by using the Shift [ and Shift ] keys. They are ranged to ensure gun convergence at 300m when the target spans their respective circle.
With the latest version of AnKor's Shaders you can also adjust the reticle brightness using Ctrl [ and Ctrl ].