Change volume of a track

Hi. I have just recorded a few guitar tracks in reaper using LePou Legion, and Line 6 Toneport as an input. The problem is that when i try to change the volume of a specific part in the track, it changes gain instead. It's like the distortion disappears when i try to turn the volume down.

I have tried changing it in the mixer, using the envelope and dragging the top of the track down.

Has this problem occurred to anyone else? What am i doing wrong and how do i fix it?