The Heaven and Earth Cursed Seals did not necessarily manifest wherever they were injected.
Otherwise, since Kimimaro's seal was right in the middle of his chest, would Orochimaru have struck him directly in the chest?
The position of the cursed seal could be controlled; theoretically, it could be imprinted anywhere. Still, just as in the original story, Orochimaru generated the three Tomoe Sharingan pattern on Anko's neck.
Chapter 121