I think we're saying the same thing mate.
But that's a refreshing change of pace from saying it's "impossible" as you did in the OP. It is possible, perhaps not to the extent you'd like, or not with the ease you would prefer (because I can still get a fairly articulate palm mute and pretty good range from my 4003), and we are now officially splitting hairs.
You made a great point: Palm muting isn't as much about hand position as it is about how much of your hand touches the strings and how much weight is used. I admit, I have to adjust my technique a bit with a Ric, but I still get the same amount of palm mute range as on any other bass. I think anyone could if they stayed with it long enough.