There is one issue with Synastry that needs to be looked though. It lasts for 20secs on the target and also the AST that used it, ok super so far so good. However, if you use any time duration increasing action on either the target or the AST (but not both), then the Synastry timer on the target effected by the increase keeps the buff for longer but their partner does not. So you could have the target on a 35sec Synastry whilst the AST is only on 20sec although once the timer ends on the AST then it disappears off the target as well even though the timers were both different.

Suggestion would be to allow Synastry to be linked so that if one target receives a duration extension, then it syncs and effects both them and the caster without them having seperate times. Alternatively prevent Synastry from being effected by duration extensions, but allow the CD to be reduced slightly to accommodate this.