Demonstratives in Tanii : THIS and THAT

All languages have demonstratives that can be used to point at objects. Unlike English which has only 2 for near and far objects (THIS and THAT), Tanii shows several additional variants.
Here are a few examples :

Example 1 : "This house"

The speaker is standing close to the object.

Example 2 : "This is a house"

Here SIIKA SI is used in place of SIIKA...

Example 2 : "That house"
A boy and a girl are talking together.
The boy is showing a house which is located at some distance :
INKA is used.

Example 3 : "That house"
The boy is showing a distant house to the girl who is standing nearby;
HIIKA is used in place of INKA

Example 4 : "That house"
The boy is on the phone, talking to the girl about his house in which is he is not.
In this example, both speaker and addressee are distant from the object,
as well as from each other.
HIIKA is appropriate here, but not INKA

Example 5 : "That house"
The boy is showing a house located far away from him.
INTODAKA is used here in place of INKA.


Example 6 : "That house"
Both the boy and the girl are pointing at the same distant tree grove. But the boy wants to specify only the bigger trees (kahe bo sanii), whereas the girl is specifying the smaller ones (atu bo sanii). INKA or HIIKA can be used indiscriminately here.

Quite puzzling, isn't it ? Well, let's leave that to the sagacity of our readers ...
What kind of rules do you think can be deduced from the above examples regarding the use of SIKA, SIIKA, INKA, HIIKA, INTODAKA ?

Grammar