Alternative rating.

Wow, you even found the Chess Federation of Namibia =)))

This website features an online Elo calculator.
You used the Zone Rating Calculator by AoR_Trillian, developed in 2000. I couldn't find any information online about it being used for rating calculations, so its scientific basis is questionable. I doubt it uses verified Elo formulas. I suggest using the Elo rating system as the most objective and suitable option, based on scientific research. By the way, I just looked at the calculation formula on Heroes of Might and Magic – it looks very similar to the Elo rating system.