mezuzah placement help

my (reform) Rabbi says any of these places (yellow, blue, or red) are fine, but I am wondering from an orthodox or other perspectives if there is a preferred placement for my mezuzah? In the yellow there is only room for the mezuzah to be vertical, in the blue it can be just barely angled, and in the red there is plenty of room. The little wall that the red is on protrudes out as a privacy wall between my door and my neighbor’s door, so it’s not a hallway wall, but I don’t know if it’s technically a doorpost either.