I find fairly reliable (esp. in case of MT healing) not reliable enough.
A split second passed and you mash your embrace button while she heals another target - thats my impression after all.

I'm not saying trying to gain more control over embrace is a bad thing, by any means do it if it doesn't interfere with your gameplay, but I couldn't find it worth the hassle.

Granted I only have 3 kills in this yet, but in the particular case of T10 my group lets the WHM heal solo during adds while I handle Prey, DPS and the fairy does her thing to top off party members and/or the tanks, and I feel absolutley no need to force her on one of the tanks; it's a computer after all, can't beat her reaction time on party members.