Synastry

[Mendalas]

Next time you use it, watch for the additional heal pop up underneath the target. It shows up as if it was a hot tick.

[Rongway]

Your Synastry link gets the piggyback heal whether your spell targets them or another party member, it just might not be visible if your game is configured a certain way.

If you have pop-up text disabled (party member damage and DoTs), the piggyback heal won't appear on your screen because it's an indirectly generated action (caster is "other" rather than self). You can confirm the piggyback heal works by turning on pop-up text. Note that pop-up text is different from flying text (actions cast by you or directly affecting you).

[Brandedblade]

Synastry is probably one of the best gcd-focused cooldowns in the game tbh. Any issue with it is solely because it cant work on aoe heals or ogcd heals. But if you're in a situation where you have to spam Benefic II on a target, its phenomenal. It's also useful for healing two targets at once. But tbh you'll most likely use it to buff your healing on a single target.

[Rasikko]

I have that set to show pop up text, just somehow I wasn't noticing it. I see it now though, and this definitely helps a ton.