Nandi, vahana of Shiva is placed directly opposite the entrance to the shrine containing the central image of Shiva, the shiva linga. In this position, Nandi is acting not only as Shiva's guardian, but also as a constant devotee. As Nandi mimics the position of every devotee who comes to stand before the deity, he is often revered as a model devotee.

Nandi at Sangmeshwar Mahadev temple, Arunaye Pehowa Haryana.
Nandi, vahana of Shiva is placed directly opposite the entrance to the shrine containing the central image of Shiva, the shiva linga. In this position, Nandi is acting not only as Shiva's guardian, but also as a constant devotee. As Nandi mimics the position of every devotee who comes to stand before the deity, he is often revered as a model devotee. ‪Nandi is described as a very staunch Shiva devotee who will never tolerate any unbecoming word about Lord Shiva. During Daksha Yagna , Daksha spoke rudely of Lord Shiva and Nandi closed his two ears, chanting "Siva , Siva". Its believed that whispering your prayers in the Nandi's ears will reach Shiva directly. As a faithful attendant Nandi informs his master of the same. Some people do close one ear and whisper into the other, as they don't want the wish to leave through the other ear. Seeing the Shiva Lingam in the sanctum from in between the ears of Nandi is also said to be a form of worship as it is believed that Shiva is looking at the world from between those ears and head. You have to ensure you do not stand in between Nandi and Shiva while praying. There is a procedure to pray to Nandi. first touching the feet, then whispering and then going to the back. As lord Shiva sits in mediation, Nandi makes sure that he is connected with the Lord. He sits as his guardian. It's difficult to bring Shiva out of mediation and he unaware continues his mediation. It's only Nandi who communicates messages to Shiva during his mediation so that he can come out of his mediation.
Om Nandishwaraya Namah ~ Om Shivaya Namah!!