Have they ever published normal-sized Tintin volumes? The books with 3 in 1, but the size of the single issues.
The "normal" size of Tintin albums I grew up with in Belgium is around 22.5 x 1 x 30.3 cm, both for the French and the Dutch editions.
However, there have been compact editions that were printed on a smaller size paper. This includes the series "The Adventures of Tintin" published by Egmont in English with a "trimsize" of 156x221mm. (These are now in HarperCollins's catalogue; see HarperCollins to buy Egmont Books UK by Mark Chandler, 1 April 2020.) I have found the following volumes:
- Volume 4: The Shooting Star, The Secret of the Unicorn, Red Rackham's Treasure (2015),
- Volume 5: The Seven Crystal Balls, Prisoners of the Sun, Land of Black Gold (2015),
- Volume 6: Destination Mood, Explorers on the Moon, The Calculus Affair (2015),
- Volume 7: The Red Sea Sharks, Tintin in Tibet, The Castafiore Emerald (2015),
- Volume 8: Flight 714 to Sydney, Tintin and the Picaros, Tintin and Alph-Art (2015).
I assume the first three volumes are temporarily out of print. (Earlier printings of these three-albums-per-volume editions are listed on Goodreads: see Volume 1 and Volume 2.) There is also The Tintin Collection (The Adventures of Tintin – Compact Editions) in eight volumes in a slipcase, with the volumes having the same trimsize as the individual albums listed above (i.e. 156x220mm).
When scrolling through the list of albums on Tintin.com (the official Tintin website), the only edition with three comics per volume is the slipcased edition mentioned above. All other albums are only available separately.
I am not aware of similar editions in French or Dutch. There was a compact edition in Dutch in the early 2000s, but that edition contained one album per volume, not three.