[Thaumatology] Syntactic Explosive Fireball Question

[MWnRNC]

I've been tinkering with the noun-verb system of syntactic magic in Thaumatology, hoping to use it soon in my campaign. I tried to create a spell similar to the Explosive Fireball found in Basic and ran into something I didn't expect.

I did not see any specific rules in the Syntactic magic chapter relating to applying enhancements to spells, so I turned to the Trading Energy for Enhancements rules on p39:

Each +1 energy and -1 to skill allows +5% worth of enhancements

It seems that the Explosive 1 enhancement, which best replicates the properties of the Explosive Fireball spell, would cost +10 energy and inflict a penalty of -10 to effective skill! Am I missing something as to why this should be so expensive and difficult relative to the regular spell? Am I overlooking some other rules?