The main culprit is the movement speed when we approach the edge of a cliff. So because we need to be precise, moving slowly, I suggest you to use the slider option you used in Assassin creed Odyssey to adjust the player walking speed with a slider. Should be an easy one because you used the same engine (anvil next/scimitar).
let us :
GRB.ini
[Options]
WalkModifierIndex=X
It's easier ATM to approach the edge of a cliff crouching with walking speed engaged, then stand up, do just a quick press the keybind (default) spacebar, (jump animation) then spacebar once more to deploy your parachute.
this is a PC trouble only because with a Console Controler you can easily adjust your walking speed.