I had to consult Bertie Wooster on the matter of the Rice Beaufort Horse Box door. It was during correspondence with Andreas, the eagle-eyed collector in Germany, on the subject of these that I actually spotted something myself - how small the door seemed to be on this #112 model! It is not often that Corgi make mistakes but this is clearly wrong.
I include below a photo of a real trailer and you'll see the difference. I think I can see how it arose: there are several variations of this trailer and I have seen some which appear significantly bigger and certainly taller, like the second one shown below.
This door more or less matches the #112 model but the whole trailer is much taller and has a different design at the font. So I reckon the designers have started with one and finished with another!