Yes, my system involves rounding to make things not complicated at the table. I always round up as well. So a 35 degree angle would just default to 45 = 3 diamonds.
I do use through diamond not across.
If you want to be more accurate, don't cross the center pocket in your picture. Add a 7th rail across the middle of the table. In other words, the middle grid line in your picture. This brings the half table into a square shape, closer to a circle, than the rectangle.
Also using through diamond the vertex would be much deeper into the pocket.
And if you take it to the table, my system works, for me, as I explained it. Even though the math isn't perfect.