Actually, some people have tested the amount of pressure needed to trigger the gestures ‘Peek’ and ‘Pop’ and the 6.666667 provided by the API corresponds to the first gesture, the ‘Peek’ with the lighter 3D touch. (source: https://twitter.com/jormy/status/647804265260580864)
I wouldn’t say you have to apply a pretty serious amount of force, given the fact that the ‘Pop’ gesture is almost double of the force (around 350 grams for ‘Peek’, around 600 for ‘Pop’).
So even though Apple did a good job providing an API sooner than in the past, when compared to features like Touch ID that took 1 year to be available to developers, they still did a poor job in the sense that:
- They did not provide the standard values used in ‘Peek’ & ‘Pop’, i.e., once people get used to the standard for action 1 & 2 (~350 & 600 grams respectively) using an App with a custom implementation which has 3 interactions (normal interaction/’Peek’ like/’Pop’ like) there is no way for a developer to code for the same values a user is accustomed to; Obviously implementing ‘Peek’ & ‘Pop’ in your app gets the right values and the same behaviour throughout the OS, but implementations using the force API won’t;
- The API does not provide values higher 6.666667 for now like you mentioned, even though the hardware is capable of doing so, as proved by the ‘Pop’ gesture.