For the purposes of education, I think maybe Berserk (or others) could benefit from understanding what the "66.42 degree" angle of 220mm actually means in terms of calculating the line of sight thickness.Perhaps our friend confused the value because 350mm RHAe in a straight line at 2km is what his country's Arjunk aspires to.
It's possible that he just made a mathematical mistake in this case, even if he may not have been coming from anywhere near a neutral pov to begin with..
66.42 degrees is sloping from the vertical, so for armour 220mm thick, one way to approach it is to use 90 degrees - 66.42 degrees = 23.58 degrees.
Using that angle to do the simple arithmetic and drawing a right angle triangle, we will be using sine, while the opposite measurement will be 220mm, and the hypotenuse is the "line of sight thickness" we are trying to solve for.
Bringing us to Sine 23.58 degrees = 220mm/Hypotenuse,
And in turn Hypotenuse = 220mm/(Sine 23.58 degrees), and thus reaching 550mm as the LOS thickness equivalent.