Default Lit Translucent Particles - still lit Outside the Light Cone

Default lit particles set to the translucent blend mode,
are still being lit, even outside the light cone.

I have reproduced this issue with multiple particle systems.
This is how it should look, blend mode is masked.

Now set to translucent, the light bleeds outside the cone.

I am using unreal 5.3.2, no GI / Lumen, not an AA issue.
Any help is much appreciated.