45.6%, I think
If the angle was 45 degrees, then 50% of the circumference of the ice cream would be inside the cone.
But the real angle is 41. 41 = (41/45) * 45
So if we multiply 45 by 41/45, we get 41. In the same way, if multiply the "50%" by 41/45, we get the percentage of ice cream circumference that is in the cone.
50% * 41/45 = 45.6%