Clarifications to the GURPS Magic System

This is taken from the "Official" Clarifications to the GURPS Magic System for Classic GURPS with notes to bring it in line with 4e.
== Calculating Spell Costs ==
If a spell can be cast at an increase to base cost to get a greater effect, the increased energy costs are calculated first, before any reductions in skill are figured. For example, a mage who wishes to cast a spell that normally costs 8, 3 to maintain at double cost (16 to cast, 6 to maintain), and has skill 25 with the spell would pay 13 points to cast the spell, and 3 to maintain it (Cost = (8x2)-3 = 13 to cast, or (3x2)-3=3 to maintain). He would need skill 40(!) to cast the double strength version of the spell at 0 cost.
Category:Rules
== Ceremonial Magic ==
When a spell is cast ceremonially, spectators must personally believe in and feel strongly about the outcome (positive or negative) of a ceremonial casting in order to have any effect on the fatigue available.
==Combining Spells==
Work out the cost and time to cast both spells without including any modifiers for skill, then add the costs and times together. Then apply skill modifiers for the lower skill to the total cost and total time, and roll against the lower skill. For example, if Spell A takes 3 seconds and requires 5 fatigue, and Spell B takes 1 second and requires 3 fatigue, then the total is 4 seconds and 8 fatigue. If a mage knows Spell A at 15 and Spell B at 30, he would apply only the modifiers for the lower level (15) to these figures, giving a casting time of 4 seconds and a cost of 7 fatigue. He would roll against skill 15.
==Spell Travel to a Target==
A spell always travels from caster to subject via the shortest route that contains mana. If any of that route is in a low mana area, there is a -5 to skill; if there are two routes and only one crosses low mana, the one with the lowest total skill penalty (for distance & mana) will be taken. Distance penalties (regular or long-distance) are figured based on the actual path taken, not the straight-line distance from caster to subject. This means that a caster can affect a subject who is separated from them by a no mana zone (NMZ), provided their skill is high enough to absorb the penalties for casting around it. Note, however, that if either the caster or subject are in a NMZ, no spell can be cast.
*Comment: The flaw here is the mechanics only work in a plane not three dimensions. In settings where mana zones have a certain height things get interesting and a spell can "jump" the NMZ.