One similarity that bothers me between the Delphi and Evansdale cases is crime scene proximity to a major highway system.
There's Interstate 380/hwy 20 directly south of Meyer's Lake in Evansdale, and the Hoosier Heartland Highway just west of the Monon High Bridge Trail. I know the Evansdale girls were moved to another location, but if it's a SK, and that was his first murder, maybe by the time he got to Delphi he didn't want the hassle or risk of transporting.
Anyway, it's probably not significant, but when I look at the maps, that's the first thing that stands out. It makes me wonder about the side roads around and under those major highways, too. Someone traveling a regular route, for whatever reason, and it involves taking exits on and off those highways routinely, and he happens to see girls alone in wooded areas...
Also of note, there's a waterway (Cedar River - IA, Deer Creek - IN) nearby in both cases, along with park grounds, bridges that cross the waterway, and nature trails.