Im really confused now, My Medial-axis operation was done with a 15 degree V bit which left me with sloped walls. which is what i wanted. When I do Horizontal Milling with a 1/16 inch EM I get perfect vertical walls, exactly opposite of what your saying. When I Pocket Mill and use an offset it leaves the Medial wall cuts alone and just flat cuts , and removes material left over to clear the bottom of the V.
So the horizontal milling follows the contours of the canvas. If your canvas has sloped walls (i.e. draft angle) then it will follow that The Pocket Milling operation contours the Contour Z height you specify and uses that to generate a set of cuts down to the Max Depth, at Cut Depth increments for each cut level.
The Medial-Axis Carving, Pocket Milling, and Profile Milling all derive a contour from the canvas at a specified Z plane, their Contour Z. For a pyramid this means that a higher Z means a smaller square will result for the cutpaths to be generated around.
The Horizontal Milling operation, in contrast, does not use a fixed Z plane that the user specifies to generate its cutpaths. Instead it generates multiple planes of cuts that conform to the canvas at each of those planes' Z depth.
For example, here's the canvas I'll be demonstrating with:
Here's a Pocket Milling operation that is using a Contour Z of 75% (0.375" from the bottom for a 0.5" thick canvas):
Here's the same canvas and same Pocket Milling operation but with a Contour Z set to 25% (0.125" from the bottom for a 0.5" thick canvas):
The Contour Z parameter is what is important to the three operations I mentioned.
The Horizontal Milling operation, by comparison, will adhere strictly to the canvas (along with whatever Leave Stock is included, but for demonstration purposes I'm using a Leave Stock of zero):
Does this help make things clearer? If I'm missing something I think if you could share some screenshots that show operation parameters that would help clear up any misunderstanding on my part. :)