I recently asked our local shop whether their new $40K tuning machine could do a base bevel, and was told only the edge should be beveled.
All other shops I have asked over the years say the same.
30 years ago I worked at the Copper Mountain repair shop, where we often tuned skis for racers. Our shop was taught a base beveling technique where both the edge and the base were beveled one degrees, so that the file actually beveled both the base and the edge about 1/4 inch in from the edge. A shop in Frisco, which only did ski tuning, primarily for racers, taught us this technique. The angle is achieved by wrapping duct tape around the end of a panzer file. I also side bevel 1 degree to keep the edge at 90 deg.
I have used this technique on all of my skis since and find that the ski is more forgiving, and that I feel stabler at higher speeds. Also, there is then little need to detune the tips and tails.
I'm just wondering if this tuning technique was used elsewhere 30 years ago and whether it is still in use today. It sure works for me.