I think it was further west based on the comment in the Silmarillion when the host of the west (Valar) went to protect the elves, "melkor met the onset of the Valar in the north west of middle earth and all that region was much broken. But the first victory of the hosts of the west was swift, and the servants of melkor fled before them to unumno. Then the Valar passed over middle earth, and they set guard over cuvienen, and there after the quendi knew nothing of the great battle of the powers, save that the earth shook and groaned beneath them, and the waters were moved, and in the north there were lights of mighty fires."

That last sentence suggests that the siege of utumno lit the sky north of cuvienen, since the elves were guarded at that point but had not began their travels west. Utumno should be closer to due north of cuvienen as a result.

I think it was further east based on the comment in the Silmarillion when the host of the west (Valar) went to protect the elves, "melkor met the onset of the Valar in the north west of middle earth and all that region was much broken. But the first victory of the hosts of the west was swift, and the servants of melkor fled before them to unumno. Then the Valar passed over middle earth, and they set guard over cuvienen, and there after the quendi knew nothing of the great battle of the powers, save that the earth shook and groaned beneath them, and the waters were moved, and in the north there were lights of mighty fires."

That last sentence suggests that the siege of utumno lit the sky north of cuvienen, since the elves were guarded at that point but had not began their travels west. Utumno should be closer to due north of cuvienen as a result.