Shower Riser Rail

I have been trying to remove an old shower riser rail as it needs replacing. There's a gap at the top where I can pop a philips screwdriver in & it appears to bite & turn but is not loosening it at all. I do have a cordless screwdriver but with the extension piece in place, it won't fit into the small gap. Any tips on how I can get this off the wall please?

Destroy the plastic and pull off then you can get pliers or similar on the screw head to remove.

Thank you. Will try what you've suggested