The WX500 can't tell the distance anyway, really. It uses some simple analysis of the return intensity, plus some kind of spectral dispersion, to have a stab at it.
I have often flown towards one single huge CB, about 50nm away, at say FL180, with vis of about 200nm all around, and it showed the strikes accurately on azimuth but well dispersed in the distance being depicted, from say 20nm to 100nm. I've got some great photos of just that.
It is very useful all the same, if you get stuck into something. The rest of the time it is great for scaring passengers
