It is 1/2. Looks like Jaete just hasn't updated some of the %, in particular, Cone of Cold, Blast Wave and Dragon's Breath should all be 19.3% (1.5/3.5*1/2*.9).

As for Pyroblast, it's easiest to consider the DD and DoT portions as two seperate spells.
The Pyroblast DD receives 115% of +dmg gear.
The Pyroblast DoT receives 20% (5% per tick, 4 ticks) of +dmg.

Pyroblast used to make sense; it used to be 6/3.5 * 75% for the initial damage, and 12/15 * 25% for the DoT, where 75% and 25% are how the base damage is distributed. The initial damage coef was changed to 115% in a patch recently (warlock's soul fire coef was changed similarly), but the DoT part left as it was.

Figured I'd throw me two cents in and say that this thread should include the order in which multipliers and additive bonuses affect spells, since it seems relevant. From my understanding its as follows.

(((Base spell+Additive mods on self)*Multipliers on self)+Additive mods on target)*Multipliers on target

Also, scaling based on level only has an effect on your side of the equation, anything on the mob gains full value no matter how low level a spell you use. This is the primary reason my paladin can still down rank rather effectively, because blessing of light is a bonus that applies regardless of spell level. The above formula has been tested also.