Having some hassle with my Estate...
I ran an RST box and various other BC boxes no problem with a AP Racing paddle clutch.
Heavy and with a low bite, but perfectly drivable.

When the most recent box failed it was replaced with an IB5 box from an RS1800.
From the word go the clutch operation hasn't been right though as the bite point is effectively lower then the furthest point of the pedals travel.

Clutch quadrant was the first suspect, but it was replaced today with no change.
Everything seems fine, but there's just not enough clutch travel! Any ideas?

Spec:
Mk4 Escort Estate
ST170 2.0 Zetec on Weber Alpha throttle bodies
IB5 box
AP Racing 220mm Clutch
Standard quadrant and cable