Hi Cerestan, I seeing what you're saying. Let me replicate that over where I am and I'll get back to you here on the forum.
I'm suspecting that there is a reason why MIDI and sample tracks are not mutually interchangeable; MIDI tracks are meant to trigger external instruments...like synths and other hardware. Every piece of external gear has different parameters which respond to MIDI messages differently. The MIDI message which changes the "envelope release time" parameter on one synth may not have the same effect on another synth.
So it's not really a "mistake" per se that the parameters of the SP-16 do not correspond to the parameters of external gear. And there's no "ideal" way of copying and pasting pattern data from one to the other.
Let me take a quick look and see what I find.