Basic break$-$even analysis typically assumes that:

both costs and reverves are made up of flaed and variable portions.

varistle costs and reverves increase in direct proportion to the unl$-$men production

revenues increase in direct proportion to the wolve of production while costs increase at a decreasing rate as production volume increases.

costs increase in direct peoportion to the volume of production while revenues increase at a decreasing rate as production volume increases because of the need to glee quarely dicounts.

All of these are assumptions in the basic break$-$even model.