Your mixin performs 32x32x32 #getBlockEntity calls whenever you take fall damage or get a status effect which isn't good for big minecraft servers. The hit is quite noticeable in the AOF3 public servers in this Spark Profile.

Another good solution for this would be to have a per-world collection with all the active sigils adding themselves every tick and then clearing it at the end of the world tick. Then you would be able to use that collection to check if there's a nearby sigil without going through mojank's code