Rolling Thunder impossible to perform

I tested Rolling Thunder to see when it should be triggered for 2H heavy attack. In summary: (this may change due to patches)

• This only seems to work for a fully charged (2 charges) heavy attack. I couldn't trigger it for a single charge with 2H (or the timing is different)
• The trigger can be a press or hold of the attack button
• During the heavy attack animation of the 2H, you can observe your weapon slowing down for a moment when it reaches the rune icon. This is what you want to aim for to trigger Rolling Thunder.
• The trigger zone starts when the center of the head of your 2H weapon is just past the top corner of the rune icon during the second swing. (when camera is behind the player)
• The trigger zone ends when it moves a bit past the rune icon's top corner (when camera is behind the player character) although it's difficult to confirm with consistency
• I tried to visualize with a picture below the exact moment when I aim to click/hold my attack button (after which Rolling Thunder was triggered)
  
  • This screenshot is taken with the camera tilted up fully. A different camera angle does change the perspective a bit in relation to the rune icon position, but it's the same position I aim for.
• During actual combat it appears to be a bit easier because the moment you want to trigger Rolling Thunder is when you hit your enemy (with the related visual and audio feedback on that hit during the second swing).
  • Tested with camera behind the player and enemy in front of player.