What matters is the taper angle (0 45 90)? (complete camber / half and half / complete toe)
However, since the pivot angle for the trailing arm is around 30 degrees, there will always be bump steer from the rear; Ford purposefully built it this way.
This is also how the BMW Z axle works.
In a PURE back axle, the rear wheels track inside the front wheels while turning, and the front wheels take a greater side load (due to the larger diameter circle they take), resulting in understeer in the limit (BAD). Having some rear steer due to roll (the inside wheel is lightly loaded and simply skids) evens out the side load and makes the car safer.
Because they were built for a rear suspension with the trailing arm pivot across the vehicle and no rear roll steer, the cheap modified tiny dampers that became zimerides couldn't control the back end.