Right now, even though it's supposedly got 1 range more than spitters, they actually outrange it from many angles. I'm guessing this is because they only need to hit the edge of it wheras it fires from the center or something like that, but whatever the case - it gets shot without retaliating sometimes. If it has +1 range that does not occur.

Try putting a piece of belt facing towards the turret right at the edge of range. It'll pull spitters into range.

Sorry for the long silence, I gave it 1 more range but have not tested it but it should work.
Thanks for letting me know :)

I have already researched turret, so u mod wont allow me to craft, u may wanna fix that for those who install the mod after having researched completed!