Previously has a 9090 from Whitefriars and, from my recollection, the sides were rounder and convex, rather than concave, if you follow my meaning! It was more like a slightly squashed circle! I also cannot remember the strong ribbing beneath.
However, Whitefriars copied many designs (allegedly) and this may be one of them that they adapted to suit their own style.
Great to have a constructive debate.