I'll rarely rely on Light of Healing to heal during a massive battle unless I'm confident it's safe, i.e. all monsters are laid out. I'll run right up in the Knight's face and cast it. 75% of the time, they'll still go for a downed attack on the monster, thus evading my heals. Or hell, I've partied with several Knights that refuse to stop for heals even when we're just moving around to another area.
One thing that a lot of people seem to forget is that my responsibility as a healer is to keep you alive by making the healing available to you, and that's it. Beads are tossed around in abundance and Light of Healing is casted in relatively close range to you. I am not, however, going to force-feed you the heals. If I cast any healing spell in your vicinity and you do not make the effort to get it, I will turn to someone else as I'll deem you a waste of mana. Simple as that.
Basically, if you're low on hp and you see beads, make an effort to get it even if it wasn't homing into you. Healers have no control who they chase, it was *probably* intended for you if you needed healing. Maybe you're fighting a mob of monsters, but they're currently on the ground. Stand still for two seconds to get some hp back, or maybe even (and this may seem extreme) move two steps to the left into the spell or something. Learn to recognize what healing spell looks like what. Prayer is not the same as Light of Healing, you do not need to hug the Healer to get the hp. Doing so is probably going to get the Healer hit which means spell canceled.
Basically, to summarize, it's the healer's duty to make healing accessible to the party members. The other party members, however, have the responsibility to make the effort to get healed. Accessibility varies between healers, some stay in the back line, some will deliver heals relatively close to the front lines. Just learn how your healer does things and don't be an ass.