Oncall is a bit special, usually counted as partial time work for time spent not responding to calls, or with overtime rates for time actually called in.

At Google SRE we had a flat ratio regardless of whether you had a page or not.

The idea was two-fold: reduces paperwork, and incentivizes the SRE team to reduce alerts that have to be dealt with.

In any case, my main point was that anything that prevents me from having a beer or going bungee jumping is 'work' in my books. Though, obviously, there are different levels of intensity.