I want to do some calculations to see which mines I should upgrade, but I am so annoyed at the game limiting the number of digits to ~2 everywhere. Did someone dig up the productivity of mines according to level ?
Gaspo produces 0.99, then 3.12, then 6.16, then 11... are there more exact numbers somewhere pleasee ?

As per the wiki, its the following:

(0.3 * Level ^ 2) + (Level + 2)
If mine's level is 1, multiply result by 0.3. If mine level is 2, multiply result by 0.6. If mine level is 3, multiply result by 0.8.

See https://war.app/wiki/Mines for a full list of values and a breakdown of % per mine.