Maybe it's a problem with Reaper's osc feedback or a reaper configuration problem? To read the parameters of this plugin I had to validate:
<Param> <FX parameter list> <Parameter Modulation ...> ...
Is there anything else to do to receive the parameters beyond the first 16?
I know the OSC documentation and I use it for other applications
http://blanchemain.info/Documents/Musique/index.php