It doesn’t have to be 45-105 only but it’s a common standard, as is 5db increments. To be perfectly honest, I can’t remember all the reasons. I just follow it as a standard. But it’s the one we all use, so it makes it easier to compare notes/graphs.
60db being the window size is what’s most important.
But think you’ll find the opposite to be true in that it won’t smooth the graph.
Maybe
@shadyJ wouldn’t mind a quick nutshell version.