"When you gain Tidal Waves, you have a 8% chance to reduce the mana cost of Chain Heal by 75% for 10 sec."
Since CH grants 2 stacks of TW and does not consume or benefit from TW it seems to me that this proc is on the wrong ability. Basically you have to waste your 2 TW stacks to make use of the proc, which seems counter productive. Little synergy we had between our healing spells is further crippled by forcing this proc in our 'rotation'.
EDIT: Let me explain a bit more: I like the idea behind TW amplifying other abilities to force you to mix up your abilities and promote synergy. Cast riptide before your HS / HW's, etc. However, CH does not fit into this model at all. I would much rather see CH be affected by TW (preferably reducing its abysmal long casting speed) and consuming a stack than having no benefit and generating 2 stacks. Especially considering you already need to have a Riptide running on the recipient (preferably multiple) which already causes TW clipping/wasting on CH cast. The set bonus only further increases this disparity in my opinion.
Either change CH to consume TW for benefit instead of generating or have TW cap at something like 4 or 5 instead of 2.