My anecdote is the opposite: I never get the hour long ads when my tablet is sitting there, only when I'm holding it. I always thought they knew the long adds were playing to an empty room, holding my place in the video till I came back to skip, and YT was deliberately trying to coax me back to watch with short ads.

I also let the hour long ads play when I'm holding my phone (just to mess with the algorithm) so maybe that is just my experience.