I use my blackbird at a fairly neutral angle, maybe just a touch steeper...like an extra 5° or so.
That works beautifully for me.
Zero harshness and full efficiency.
If I tilt the handle up a little, I feel some harshness without any additional efficiency.
I should mention I use BIC blades, which are about as sharp as feather blades.
When I use Wizamet, the angle is less sensitive as the blade is ultra smooth and a little forgiving to razor angle.
That works beautifully for me.
Zero harshness and full efficiency.
If I tilt the handle up a little, I feel some harshness without any additional efficiency.
I should mention I use BIC blades, which are about as sharp as feather blades.
When I use Wizamet, the angle is less sensitive as the blade is ultra smooth and a little forgiving to razor angle.