What determines your spirit guide?

In Myst IV, what determines your spirit guide? I'm on my second play-through and I got Water again so I was wondering how it can be changed? Just to be clear -- I know what to do after you get your spirit guide and what the spirit guide affects, but I want to find out what choices in the game lead to the protectors giving you a certain spirit guide.

Explanation based on information from ubi forums and mystlore:

Score is a number between 0 and 3, starting at 1. It determines which spirit guide you'll get and is affected by following events (most of which increase it):

In Tomahna:

• Take a photo on the monorail: 0.1
• Finish the sound puzzle with Atrus: 0.1
• See Yeesha's gecko: 0.1
• Watch Yeesha play her flute: 0.1
• Contact Atrus with the crystal viewer: 0.1

Using linking books:

• Link to both Haven and Spire from Tomahna: 0.125
• Link to Tomahna from both Haven and Spire: 0.125
• Link to Serenia from Tomahna: 0.125
• Link to Tomahna from Serenia: 0.125

Other actions:

• Spend time in the game: 0.5 total for 20 hours (0.0004 per minute)
• Use the Amulet: 0.5 total for all 101 flashbacks (0.0050 per flashback)
• Use the zip feature: -0.5 total for 30 uses (-0.0167 per use)
• Use the hint map: -0.5 total for 25 uses (-0.02 per use)

How score is mapped to title, description and spirit guide you get:

• Child of Fire: 0 to 1

  Drawn by the excitement of new experiences, always seeking adventure over stasis. Sometimes your desire to succeed makes you miss the deeper meaning but you always find the answers you seek when you really want them.

• Child of Wind: 1 to 2

  Attracted by challenge and diversity. Always moving swiftly to the heart of the matter yet willing to take the time needed to understand it.

• Child of Water: 2 to 3

  You appreciate the beauty and richness of life around you. You are confident in your ability to succeed but willing to seek help when answers seem elusive.