Glow effect radius shouldn't need scaling by devicePixelRatio to get the same apparance on retina devices

I've recently been revisiting some old code last built with earlier Qt5 releases and updating it to Qt5.6.1 (not sure exactly which version of Qt5.x I was updating from, but it was before a version or two where the Glow effect was significantly overhauled but broken for a while; see QTBUG-47448)

Anyway, I've been a bit surprised to find that after the update, some Glow effects looked significantly different on OSX (&Linux) and iOS.

In all cases I was using a Glow with radius of 16 and samples 32, but on iOS the glow looked much "thinner". I was able to fix this by exposing devicePixelRatio to my QML and multiplying the radius up by that, after which things look much more similar.

I'd expect radius to be defined in "logical" pixels, like most everything else in QML... but what I'm seeing seems to imply it's defined in device pixels.

I'll add some screenshots at some point.