Measuring the relative softness/hardness along the length can be quite misleading. Instead pinch it in the centre between thumb and forefinger on bulb and cut edge. Also I am unsure whether the bulk Duraflex is any different to the pre-angled Liquidator Rubber. …and yes you’ve nailed the ‘flexion’ with the added albeit minute width difference. The clips are designed to work with the Moerman rubber giving 1-1.5mm of exposed rubber from clip to rubber edge.
Two different factories? Quite possibly… and if Gummifabrikken haven’t got their finger on quality control? Who knows…
