How level to get tile backer boards?

[Tony K]

Afternoon. 

I am about to fix tile backer boards to the stud wall shown in the attached photo. 

 

In fitting the bath, the plumber pinned in place the backer boards you see. The bottom of the boards go down past the top of the bath by an inch or so. 

 

You may notice that the horizontal frames of the pocket door housing (on the right of the picture) protrude past the face of the metal studs (on the left of the picture) by about 5mm. The wall is only 1.6m wide, and when I hold a straight edge to it, it seesaws. 

 

Is that degree of deflection acceptable for a tiler? 

 

Or do I need to cut out the existing boards, build up the stud faces and fix them back on? That seems to defeat the benefit of the boards going down past the bath as they currently do. 

 

Cheers! 

[Mr Punter]

The studs need to be in a line or they need packing.