In relation to the radius given on tool-tips for different spells I noticed that Earth Enchantment has 6m but only affects my groupmate if he is less than 3 steps from me .
Either my guy takes massive strides or the radius of some spells needs adjusting!!
Playing a caster and tank combo it's often the case he gets out of my aura ranges. Thankfully Heart of Oak has 18m radius (giant strides and all).