I hope someone can advise me. I'm trying to insert an F40 bulb (1.5" diameter, 4' long) into the socket shown below. With every other fluorescent socket in my home, I simply orient the two bulb pins vertically, push the bulb up into the socket, and then rotate the bulb 90 degrees. But as the photo shows, I can't insert the bulb vertically, because that path is blocked. I must be missing something obvious... can anyone help me? Thank you!