I have the same lines with my Lowrance on DI and out the port side on Si.
Last summer after moving my transducer board and transducer closer to the center of the the boat and lower,I figured I'd have it,nope same lines. So I did what Ricki said,screwed the transducer on a 1x4 and C clamped it to the transom, I tilted the big motor and kicker out of the water and went testing.I ended up having to move the transducer about 4" below the bottom most part of the center of the boat....but the Si and Di pictures were perfect.
I haven't decided if I'm going to mount my transducer on a tilt stick yet or not for this coming summer....FYI I have a aluminum boat also.