The relative steepness or flatness (more inelastic / more elastic) of the demand curve, affects the amount of revenue generated. Demand that is relatively elastic indicates that consumers have more substitutes avialable or that the good is a large part of their budget. These consumers are more price sensitive. You can model this my moving the Demand slider to the right. With increase price sensitivity, quantity demanded falls by a larger amoung with the imposition of the tax and thus the amount of tax revenue generated decreases. Markets where demand is relatively elastic are not good markets for using excise taxes for revenue porposes. Also, when demand is relatively more elastic, the deadweight loss is greater -- there is more distortion in the market.
When you move the Demand slider to the left, you will notice that the opposite is true. If demand is relatively inelastic, quantity demanded: a) falls by a smaller amount, b) the same tax generates more revenue and c) there is a smaller deadweight loss -- less distortion in resource allocation.
In the real world, you will find that excise taxes are often imposed on markets where consumers are less price sensitive like; tobacco, alcohol, telecommunications services, etc.