Quick question about attaching Batons to walls..

[enigma27]

Hi all.

What's the general rule of thumb when attaching Batons to walls in terms of screw length?

I always used screw length twice the width of the baton but now I'm being told 2.5x.

I'm putting up some 25mm baton at the weekend and now unsure what size screw to go with brown plugs

 

[enigma27]

It's going to be fit attaching 9.5 mm plasterboard to

 

[enigma27]

Thanks