The Angel's core lies adjacent to the Eva's head. Eva's body is completely entangled by Sachiel's rubbery exterior.
Keisuke-kun: Maybe Sachiel is smart enough to know that to do the most damage he should put his core as close as possible to EVA-01.
Reichu: If he was REALLY smart, he would've shoved his core against her core and not her head. Ah, well, being on the brink of death leads to a lack of good judgment, I suppose. (Unless you're EVA-01, of course.)