How do I get my Vocal Sample to respond to MIDI IN commands?

[repeater]

Hi all,

I can't get my Vocal Sample to respond correctly to MIDI commands sent from my DAW (Reaper).

Screenshot: https://ibb.co/sF3GQRv

As you can see from the screenshot, I've set up one MIDI Channel to send data out to two devices:
- Yamaha CS2X synth (green track)
- Volca Sample (blue track)

The pattern is just a few notes played at different velocities (levels), varying from 51 to 105, as you can see from the event log.

The Yamaha synth (green track) receives the note and the volume level data, as you can see from the variation in the waveform.

The Volca Sample (blue track) receives the note data, but doesn't respond to the volume level data, as you can see from the lack of variation in the waveform.

If I understand correctly, each Volca Sample part is assigned to its own channel. In my case, I've assigned the MIDI pattern track to send on Channel 4, which triggers Part 4 (a snare sample, in this case). The Sample responds to the note data - why doesn't it also respond to the volume data?

For the Global Parameters on the Sample, I've got:

MIDI Clock Src = Internal (otherwise, the pattern gets triggered)
MIDI RX ShortMessage = On

I've been wrestling with this for two days, and after looking through several discussion forums, watching YouTube videos and staring at the manual, I've run out of ideas. I admit I know very little about MIDI, but I'm hoping there's an easy answer to this and I just haven't figured it out. Please advise! Thank you!