Shadow Wave's beam always starts at the unit's origin, which is in almost every case below the unit. For ground units it's between their feet, and for flying units, it's below their model. The Beam's end point is the chest area of unit it jumps to.

This causes the beam to break visually. It looks like individual beams coming from each unit, instead of being one continues beam coming from Dazzle.

The starting point of the beam should be chest of the bouncing units.

Note: This is only about he visual effect. The spell should use absorigin when searching for nearby units, but the beam should visually start from the chest. If you make the search area centerd around the chest, then the search areas will be inconsistent and be affected by the units' animations and whatnot.