Just a thought. If it was me having this problem I would crank VR16 the othr way to see if it made a difference at all.
If it were me I would observe my modulation as I turned VR16 just to make sure it wasn't in no man's land. Is it a good idea to crank it all the way up? DTB had mine set for 100% modulation and VR16 still had travel to go before it reached it's max position.