Seems that my first idea was correct then, but I think I should make something more "universal". Like: If X value is 90% of the Y value is better, isn't it?
Let's suppose that we have 100 as X and 95 as Y, then we've 95% of the main value, so it's kinda approximated, or is it the same idea as doing X - Y < 5?
5 - 3 is not the same as 50000 - 30000. Better use a percentage of your choice.