I’ll tell you once I have it all installed Macca, It’s possible that it works as you suggest, but my belief is that in manual mode you still use the foot brake & as soon as the brake lights come on (i.e. very light/ineffectual vehicle braking) the van brakes come on at the pre-set dialled in setting. I am uncertain if turning the knob once braking has commennced will increase/decrease van braking in the same ay as the Tekonsha slide does.