Under the in game config under -> Client Settings -> HUD -> Target HUD Style
There are two settings with the same description "Text Opacity". I believe the first one should be labeled "Reticle Opacity"

This may have been intentional, but for me it was not apparent and confusing. I only found which one manipulated the reticle by trial and error.
-jc

Good catch

This should now be fixed in the latest release