"I specified 4096 when using mount" – Not really. You specified the offset as
1074790400. My point is mount is not able to tell if you used $((4096*262400)) or $((512*2099200)) or e.g. $((51200*20992)); and the loop device your mount created most likely used 512-byte logical sectors anyway. If 262400 is the start sector of a partition and the sectors were 4096-byte then offset=$((4096*262400)) is right, offset=$((512*2099200)) is equally right; neither specifies 4096 as anything. offset=$((512*262400)) would be wrong, but it's not clear this is what you originally used.