I have poly everywhere back and front, imo the rear polys get blamed when clearly not at fault, jesus they don't exactly have high load as they are only trailing.
The whole rear end on a sapphy or 3 door is a problem, due top budget and other constraints they had to use what was in the parts bin at the time of making, which is far from ideal.
The major problem is the rear diff hanger, even new ones are way too soft, ford then decided to compound the problem on the cars by fitting less than ideal anti rolls bars on the rear.
I run poly at rear(all fixings) but also run a poly diff mount, and a 22mm adjustable anti roll bar.
The rear is 100% slop free and sticks like glue, corners I wouldn't go round at anything much over 80/90 before are 100% rock steady at 150 now, talking of long sweeping dual cariageway stuff, doesn't even twitch.
I tried my car when experimenting without any rear roll bar, then with a poly diff mount, that alone took away 90% of the rear steering when hitting a bump mid corner, then added the arb, 100% happy with it now.
The basic design is the problem, as they are not fully trailing arms, any increase in bump/height deflection also causes a camber and toe movement, so going down a bumpy road the wheels are all over place toe and camber wise, add to this the soggy diff mount(even when new), this then alters everything again as diff/beam rises and falls in height relative to the body adding yet even more movement into the mix.
In order I would sort the diff mount first, this will give you most bang per buck improvement, then arb then bushes.
tabetha