Third creature update.

Hello everyone. In Heroes of Might and Magic 5, I created a small mod for the Tribes of the East faction, specifically strengthening the third upgrade of the creatures. However, I encountered a problem. When I upgrade creatures from the second tier to the third, it costs only 10% of the original price, which means I can purchase the third-tier upgrade for a significantly lower price than its actual value. My question is, where can I find the file that contains the script with this 10% (or 0.1) coefficient? I need help locating this file and script, or alternatively, how can I prevent upgrading from the second tier to the third, and instead allow upgrading from the first to the second tier, as it was originally intended...
Thank you in advance. If anything is unclear, I will clarify.