Basically as was stated. With the 3 idol items, and windspeakers, you get a 55% increase.
If you purchase Spirit visage or heal a target with Spirit Visage, then it becomes 86% increase. If you have Runic armor which is a 8% increase puts it up to just over a 100% increase.
Though I'm not 100% sure how the calculation does for how Spirit Visage and Runic Armor works together if it ends up being a 28% increase on the 55%, then its only a 98% increase, but otherwise it's a 100% increase if it's 20% then 8%
Either way, It's a metric shit ton.
Executioner's Calling turns it into 19% increase from the 98% increase, while a 20% increase from the 100% increase. Overall, stacking all the healing boosters you can is still incredibly potent.
EDIT: If the Healling boosters from Spirit Visage and Runic Armor are done first, then it only ends up being an 85% increase in the end rather than a 98 or 100% increase.
This means executioner's calling brings it down to an overall 11% increase when the target has grievous wounds.
EDIT 2: The wiki is kind of unclear on how SPirit visage stacks with the Idol Items. AHHH I messed up since I thought it was only a 20% increase from spirit visage, not 25%, so my calculations are correct in that with all the items its actually a 110% increase on healing to the target holding a spirit Visage. This means that Executioner's calling brings it down to a 26% increase overall.