If the ox tiger is an unlucky direction, why build an entrance to it?

The article on Wikipedia gives as examples of temples with Kimon facing north-east:

• Enryaku-ji
• Kan'ei-ji

These temples are deliberately constructed for the Kimon to face the nearby (Capitol) city, their function is to actually keep the Oni out of the city (i.e. build where the Oni would gather outside the city). Cities were built to have their Kimon protected with clusters of temples place towards the northeast. Allegedly, the spiritual power of these sepulchers would rebuff the evil flowing from the Kimon. If we look at the example of Kyoto, we see that Enryaku-ji on Mt. Hiei sits at exactly where the city’s Kimon would be.

Traditionally, many buildings in Japan have been erected with some sort of odd irregularity towards the northeast. In many cases, this peculiarity takes the form of an L-shaped indentation that is said to keep out the oni and other spirits. Even the Kyoto Imperial Palace has notched corners on the northeastern exterior.

On a final note, I should probably mention that the Kimon built in this direction will typically have a "spirit screen", i.e. a structure right behind the gate blocking a direct line of entrance:

It is believed that Oni and other spirits can only travel in straight lines. You will find this "spirit screen" in many Chinese and Japanese traditional buildings, including ordinary family houses.