In this picture you can see that two mezuzahs were placed on the right side leading into the more important room. I will now explain why this is so. I will note that this is also the common Chabad practice.
In the sefer
Nesivim Besadeh Hashlichus (Rabbi Raskin, a Dayan in London) p. 90 writes that when there is no heker tzir (and it is possible to reach to the intended room from 2 different directions) and it is not a front door, we find 3 opinions on how to judge the right side for a mezuzah.
1 the closest entry from the outside public thoroughfare i.e. the chitzon via pnimi logic i.e. the house has two entrances leading into it, we take always from the entrance from the closest to the public domain and do not consider what is important 'chashuv' or not (
Siddur Derech Chayim)
2 More common entrance, 'rov tashmisho' (
Gidoli Hakosdesh 289:7)
3 Importance, 'chashivus' (
Daas kedoshim 289:11)
The author writes the common practice (in Chabad) is like the 3rd approach, and he quotes the Kovetz Razash p. 58 (authored by Rav Shimon Zalman Dvorkin, a reputable Rav of Crown Heights, who passed away in the late 80's) .
He also writes that to his opinion the kovetz Razash rule of following importance 'chashivos' is referring to when one has two way access from either way, in such a case we do not choose 1 or 2 but davka chashivos. If however the chashuv room leads into a tafel room and there is no other entrance to that room but through the chashuv room similarly if the main entrance is through the chashuv room going into the less chashuv room than we go after chitzon pnimi klal.
Although the author did not go into the reason it makes sense. For the following:
1 if one had a short hallway 1.5 meters long, and two door less doors, on one side leading into a kitchen and the other side leading into a dining hall would we say that each mezuza should face opposite directions? no, we take one direction for both of them even though you can say that the kitchen is more chashuv than the hall and the dining room is more chashuv than the other side of the hall.
2 We cannot compare are non compromising svara of heker tzir (besides for main entrances) to chashuv i.e. the rule is not always followed blindly because heker tzir has to do with the baalus of the door while chashuv is an interpretation in 'derech biascha'. Seemingly the shach is also not a proof,as mentioned the makor of chashivos is from the daas kedoshim which was not talking about the situation of heker tzir.
In cases when it is not derech biascha for example when there is no other entry except from the chashuv into the less chashuv or the main way is from chashuv into non chashuv we go by the 'derech biascha' bepashtus.
