I use reset=combat, for Lava Burst and Chain Lightning, since these have hard recast timers.
And reset=target, for Flame Shock.

However, with Flame Shock as the first macro, it attempts to execute first.
If you are on a comma stage, it allows for another (later) macro to fire off.
If it is on cooldown, and wants to cast, nothing else can until it fires off, hence the (up to 6) seconds of delay.
There are talents to reduce this, but that's generally more of a PvP spec.
I had the same issue putting Chaos Bolt, in front of Immolate/Conflagrate.