HX Stomp/Mission SP1-L6 issue

[velvetkevorkian]

I picked up a second-hand SP1-L6 (that's the expression pedal with toe switch) and I'm struggling to get it to work correctly with my HX Stomp. 

 

Basically it seems like I can get either the expression OR the FS on the tip. e.g. here the toe switch works as FS4

 

 

While here, I can assign exp1 in my patch and see it working

 

But I don't seem to be able to get either on the ring

 

I have a double footswitch which works perfectly as FS4/FS5 with the same TRS cable, so my guess is either the switching inside the pedal isn't working properly or I'm somehow using the wrong cable? I have tried a variety of other cables I had kicking around without any joy.

 

Can anyone suggest anything I've missed?