Shower - slow draining / replace flexible pipe ?

[Achy]

My shower was draining slowly so I took the base off, removed pipes/trap cleared all the usual hair and gunk out and it's better.

But...

From the shower trap there is a 18" flexible pipe laid horizontal in a C shape that then connects into a solid vertical waste pipe.

I figured the long horizontal bit wouldnt help with drainage so have decided to replace the 18" of flexi pipe with 6" of solid pipe between the trap and waste.

Is this going to cause me any problems? I can't understand why it was installed with this pipe ?

Any advice/opinions greatly received

 

[Bahco]

I can't understand why it was installed with this pipe ?

Nor me.

Can't see you getting any problems.