Purple Flames of Chayula and % Increases to Chaos Damage

Is percent increases to Chaos damage supposed to apply to the entire Purple Flames effect?

ie If my character has +100% to Chaos damage from passive tree then 1 Flame with Lucid Dreaming (double effect, 14%) should provide +28% (14%x2) of damage as extra Chaos damage?

Because in my testing it seems that % increases to Chaos damage only effect the base 7% of purple Flames. To use the above example,

Base - 7% x 2 = 14%
Extra (Lucid Dreaming) - 7%
Total as extra chaos - Modified base + Extra (14% + 7%) = 21%

Currently with 100% increase to Chaos damage I'm seeing approximately 21% of damage as extra Chaos instead of the expected 28%.

Some clarification would be helpful. Is this a bug or functioning as intended?