units rounding clarification

I have read that most numbers in PoE round down. Is there any general rule how to recognise what numbers are integers and if they are rounded down or up?

Is AoE radius an integer value which is rounded down?

Lets use Fireball as an example: FB has base radius 8 units, so what I believe is I need to reach breakpoints to increase its radius (in this case 13%, 25%, 38%, etc). Is this correct?

One thing that confuses me is "Fending" passives cluster. It gives total 45% increased knocback distance. Base knockabacks distance should be 4 units so this cluster would give me only 1 unit, leaving me only 5% from other unit´s breakpoint. This seems strange to me. Or am I supposed to get those extra 5% from some other source (gem quality, skill property, uniqu mod, corrupted implicit mod)?

Thanks for help

Numbers in calculations are always rounded down, however in some calculations it might end as rounded up.

Reduced skill cost and reservation are a good example, when you have 10% reduced skill cost the game will calculate 10% of your skill cost, round it down, and then deduct it from skill cost, effectively rounding up. Reduced mana gem is a multiplier, though and it rounds down.

I wouldn't get too concerned about it, it's a pretty rare occurence and there isn't a general rule, it's all under the hood. AoE radius is rounded down, like most others.

About fending, yes, I guess it does work like that, and it's pretty common, for instance, shock would require you to do 1,08% of target's health in damage to get a minimum duration shock, but due to rounding you have to do at least 2%. Maybe we'll get some uniques that will make knockback distance increase over 25% meaningful. Not many people are concerned with knockback, though, so I wouldn't hold my breath.

thanks for the clarification, makes sense. It was that 20% knocback distance "uselesness" what made me doubt about it