The upgrade description states:

> Mutalisk attacks bounce three more times up to six targets. These bounces deal increased damage and travel farther.

So how much damage does each bounce do?  Without the upgrade, each bounce was 1/3 the damage of the previous bounce.  This resulted in the last bounce dealing 1 damage. 

Am I correct to assume that each bounce is 2/3 the damage of the previous bounce?

Note: This only applies to the campaign play through of the game and does not apply to multiplayer.