The Icy Veins guide is just bad/wrong/out of date. For example.
This is just downright wrong. Below 20% FR is only using during Battle Cry, Mortal Strike is still used on cooldown but Execute is the main ability and takes priority on Shattered Defense. In execute phase we only use Battle Cry directly after CS application, then we spam Execute during (no refreshing CS during Battle Cry, just execute) for maximum damage/rage spending for tactition procs, using our 3 stack MS outside of Battle Cry in the normal "on cooldown" fashion we use outside of Battle Cry.1.3. Execute Usage
Execute is currently only used in conjunction with Shattered Defenses, or if using Ayala's Stone Heart procs. When using Focused Rage, it is pushed out entirely outside of ring procs, due to Mortal Strike taking priority.
In other words Execute phase is abandon FR, use MS on cooldown and Execute outside of that, using Execute for Shattered Defense.. Now some people might have some optimisations or more clear explanation than this, but Icy Veins is terrible as a guide right now because it's still based on the primitive understanding taken from the 50% Focused Rage period.