Machine shop forgot oil plug?

If you look at the diagram I posted, the oil galley shrinks down going towards the top. The plug is in that area. In short, I believe someone used an incorrect size plug and installed it in the part of the galley that necks down, instead of further down and away from the intersection of the galley going to the filter area. Did the shop do it? Is it something the factory did? Who knows? It looks like that passage going to the top where the sender is, is blocked, like the factory intended regardless.