Tweak_Pick_Through/Slide_Selection tool tweaks outside of set influence

The tweak-pick-through tool (hotkey v) often affects vertices that are outside of the sphere of influence of the tool. It seems as if the influence of the tool is in screen/camera space rather than 3d space. -Or ignores depth in some cases. Ex: when using tool to tweak a foot on a quadruped, if the foreground foot occludes some of the background foot in perspective view, the occluded verts of the mesh will be edited even though they are far outside of the "depth" of the tool's sphere. If the sphere is made to be large, the influence will affect "background" verts that overlap with the sphere in screen space. I have not been able to take screen captures of the issue but it is easily repro-able on a large contiguous mesh that is able to occlude part of itself. 

Also I would like to be able to edit sphere of influence in another way besides mouse wheel, so I could use the tool with a wacom pen. I will add suggestion to requested feature forum.
Thanks, I use Nvil when I have free time and it is great.

When you use pick-through tool, it is not a sphere, it is a cylinder with finite length in camera direction.

This tool may help
Edit > Customize > Tools > Common Shortcut Tools > WMB-Up/Down Simulator.