Gem Use for Fatigue/Boosting Skill

[Mysterio]

Hey, folks. I'm a bit confused on gem use as it relates to being able to cast a spell. According to the manual:

• only 1 gem can be used to temporarily boost a mage's skill by 1 to cast a single spell
• 1 gem is needed for every 100 spell fatigue
• a mage can not use more gems for skill boosting and spell fatigue than his native skill in a path

Are these all true, and is the gem limit based on the mage's native skill or his current skill prior to casting the spell (i.e., increased via Summon Earthpower, Summon Storm Power, etc.)? I have an example:

I have an E2 mage that wants to cast Earthquake. I use Summon Earthpower to get him to E3 for the battle, and then an earth gem to get him to E4 to be able to cast the spell. Since Earthquake has 300 fatigue, he needs an additional 3 earth gems, bringing the total number of gems for skill boosting and spell fatigue to 4, which is two more than his native skill in earth (E2). According to the manual, he would not be able to cast Earthquake in this manner. Is that correct?

Also, assuming he could cast Earthquake in this manner, would he have to use an additional 3 earth gems, since the spell description says the spell requires 3 earth gems?

I feel like I'm not reading the manual correctly. TIA for any help!