So for better or worse i've ended up with a scenario where my ufh pipe must zip tie to the top mat of a393 mesh but then have a142 mesh as anti-crack sit directly on top of the pipe.   My concern is that during the concrete pour a workmans welly on the a142 (6mm) mesh becomes somewhat more of a point load on the pipe.....certainly on a test piece not under any water pressure it leaves a dimple depression.   One supplier isn't concerned for the robustness of their pert-al-pert