What determines when my Apple Watch uses a haptic tap for a notification?
From this Apple Discussion:

There are variations. The 3rd party app developers have some control over what you get, but they won't have been able to check it before launch - they'll have been using a simulator.

This can currently not be changed by the user.
To turn haptic feedback of:

Open the Settings app.

Scroll down and tap Sounds &amp; Haptics.

Turn Haptic Alerts on or off.