Two 3Ω coils in parallel yields an equivalent resistance of 1.5Ω (that's what the battery sees). However, the total current (and power) is split between the two coils.
Looking at it another way, a single, 1.5Ω coil at 5V = 16W. For two 3Ω coils at 5V, the battery still provides 16W total, but each coil only receives 8W.
One effect of a dual coil carto is that the total surface area of coil to wick or filler is increased. This leads me to wonder why no one has done one using a lower resistance wire in order to increase the coil length while keeping the overall resistance in the range of "normal" cartos.
Looking at it another way, a single, 1.5Ω coil at 5V = 16W. For two 3Ω coils at 5V, the battery still provides 16W total, but each coil only receives 8W.
One effect of a dual coil carto is that the total surface area of coil to wick or filler is increased. This leads me to wonder why no one has done one using a lower resistance wire in order to increase the coil length while keeping the overall resistance in the range of "normal" cartos.