I just bought an e7D too. Haven't got to the transducer yet, but I don't think you'd be happy with it not mounted vertically.
Let's say the bottom is 10' down. If your transducer shoots straight down, it gets a return of 10 feet.
If it shoots forward at an angle, it's going to go farther, so it will read say 11', if it gets a return at all and it doesn't bounce off the bottom at an angle and keep going.