Hard to see enough of the schematic (on unit lid) in the online pics to say for sure. But my guess is the stereo FX send (loop) signal is derived before the cannel pan so while the L/R of JMP or MP1 can be panned hard left or right in the main mix, the send will still "see" them in stereo (I don't think the channel pan will affect the send (stereo bus), just the main stereo mix bus). With a readable picture of the lid (schematic) I can be definitive.
However, if you want the JMP to be dry and MP1 wet, just turn the JMP FX (loop) send off, it will then be dry and mix in as desired. You'd have to do this anyway with your other thought as it will still feed the FX bus (unless you turn its send off).
Much better to keep it stereo, the MP1 sounds much better and so do the FX.
To do a "proper" wet dry (if there is such a thing LOL), you'd set up a separate dry rig with JMP and put it between the MP1 wet cabs or similar, gets elaborate and requires more poweramps and cabs. Like I used to run my MP1 years ago, in stereo, wet and dry mix into 2 ADA slant split stacks and dry Marshall '72 50w (power soak) mono 2 x12 cab in the centre. Lots of stuff to lug for very little gain (did sound good though). If you set your rig up well in stereo, there is little or no need for wet/dry rig stuffing around. But that's me, others like to play with the idea.