Vclay evaluation using IP (Interactive Petrophysics)

Dear All,
When I calculate Vclay ( I'm using IP software), I wonder how I can calculate Vclay exactly.
I have data from neutron log, density log, GR log, sonic log, resistivity log, and the two-curves cross-plots.
I'm using the SS (sandstone) line to define my clean line, but I'm having some doubts:

1)The neutron clean line always have 0 value?

2) Can the Clean Point 1/ Clean Point 2/ Clay Point of all the methods be the same value, for example:

At neutron:
Neu Clean = 0.27
Neu Clay = 0.3


Then, I put at Density-Neutron:
Den ND Clean 1 = 2.65 (being of SS line) / Den ND Clean 2 = X / Den ND Clay = Y
Neu ND Clean 1 = -0.02 (being of SS line) /Neu ND Clean 2 = 0.27 / Neu ND Clay = 0.3

Using this ideia, at Neutron-Sonic (same doubt for the Density-Sonic), Can I use the same values to simplify my evaluation? Or the values have to be another? (Dont have relation with the values in another clay indicator)

Like (Repeating the same values of the neutron /N-D lines):
Son NS Clean 1 = 55 (being of SS line) / Son NS Clean 2 = Z / Son NS Clay = W
Neu NS Clean 1 = -0.02 (being of SS line) /Neu NS Clean 2 = 0.27 / Neu NS Clay = 0.3

Is it wrong? What's the relation?

3) At the attached image, are the lines positioned correctly?


If you have experience, please share some idea.
Thank so much.

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Question (3) image