Ethanol forms an azeotrope, and there’s a lot more ethanol than heptane- the azeotrope by definition has a lower boiling point than either compound that make it up so it will evaporate the azeotrope first, followed by the ethanol that remains- think of the azeotrope as a unique entity that is neither heptane nor ethanol in the way it behaves physically- so the azeotrope is the first fraction of your distillation that works on a constantly changing curve rather than a series of set compounds coming off at specific temperatures-
When I equilibrate a fractionating column I am moving the first azeotrope fraction to the top and holding it there until it stabilizes