Some Questions about Enchantment Spells

I’m looking at the Companion p.117. I want to convert a spell from Barrowmaze which cases a fear effect for 1 round per 2 caster levels to anyone within a small cone (20’ long, 5’ wide at origin, 15’ at end) if they fail a save. My problems are:

  1. Fear in this page is given only for 30 (!) rounds - “Target flees in panic for 30 rounds” this is expensive and I don’t need 30 rounds, only 1 per 2 caster levels. How much would “simple” fear cost?

  2. How do I model the fact that the spell does not scare monsters of 4 HD or more while working as a cone?

  3. How much will a 20’ long, 15’ wide cone cost?

  4. How much will 1 round per 2 levels cost as duration?

Disclaimer: I am not an autarch and this is all just napkin guesswork math, you should make sure the spell makes sense to you.

  1. Fear for 30 rounds is 40 spell value, commanded is 60. closest durations are 12 rounds (x1.15) and 6 turns (x1.2) this tells us commanding for 30 rounds costs somewhere between 69 and 72, putting fear at no less than 56% and no more than 58% as strong as command. This suggests that a fear lasting for a given spell duration should cost between 33 and 35 spell value.

  2. all of the enchantment spells are based on the idea of # of HD affected. They have to because most of them are completely taking out a creature, as opposed to blast effects that have continually smaller effects on bigger creatures. I’d say start 1d4 creatures of up to 4HD (x1.2) compared to up to 2d8HD of creatures up to 4HD (x2.25). With only two points of data we can’t assume much about the relationship. Ignoring the first x1, the first target set seems to cost between 0.05 and 0.2 (avg 0.08) per affected creature, whereas the second targeting is somewhere between 0.08 and 0.625 (avg 0.14) per affected target. This tells us that each target gets more expensive the more targets you have. if you assume a cone 20’ long and 15’ wide can affect at most 4 rows of people numbering 4, 4, 3 and 1, that’s 12 people, so it seems like 2d8 is a closer value.

  3. the area of a 60’ long 30’ wide cone is x5, the area of a 480’ sphere is x8. We can treat them as 2d or 3d objects, calculate their area, assume a linear relationship between area, and figure out where a cone with your dimensions would fall. That’s a little more math than i’m ready to do on the spot, but that’s your best bet (and is very likely to be wrong, but it might be close enough).

4)Instantaneous (aka 1 round) is x1, 1 round per level is x1.2, therefore 1 round per 2 levels is somewhere in between, x1.1 is probably a fine estimate.

Thanks! I’ll try that out. Meanwhile I tried something based on the rules-as-written.

Jard’s answer is superb.