On the help page for [fluid~] at the bottom left is the section relating to generators. If I enter 16 for reverbsend and change the value even to 8192 nothing happens.
I took a liberty and downloaded the Purr Data source from your GitLab page and had a bit of look at the fluid~.c code (and C is really over my head) I found these 3 lines.
fluid_settings_setstr(x->x_settings, "synth.chorus.active", "no");
fluid_settings_setstr(x->x_settings, "synth.reverb.active", "no");
fluid_settings_setstr(x->x_settings, "synth.ladspa.active", "no");
I then wondered if this was by design, because in the FluidSynth 1.1 Developer Documentation they are on by default.