Some tiny women in real life end up with very tall men. Perhaps they were going for realism.
My password is password.

True about the standing on boxes or wearing lifts etc. Brings to mind Alan Ladd… found this amusing entry in his IMDb Trivia:
Ladd's height was 5'6". To allow him to appear to be the same height on screen as taller actresses and actors, crew members placed him on boxes or ramps that were strategically out of frame. When he was making
Boy on a Dolphin
(1957) in Greece with the 5'8" Sophia Loren, boxes were not possible on the sand. Consequently, the crew dug a trench for Loren to stand in for scenes in which she and Ladd were standing and walking together.

I’ve heard where this happens and they settle but they really need to rethink the height thing. My mom used to tell me they would have the shorter actor stand on a box or wear lifts/platforms. Hollywood has plenty of actors. The Vince Vaughn/Reese Witherspoon Christmas movie was terrible but again the height thing was ridiculous. You never realize how tall most actors are until they are next to someone short.

It might just be something as simple as availability. I don't know how many times I've read where so-and-so actor or actress was the director's first choice for such-and-such a role, but said actor had a prior commitment to some other film. Sometimes they just have to take whatever second (or third, fourth, etc.) choice they can get.
In the Trivia section for
A Farewell to Arms
, it was noted that Fredric March was originally set to play the lead, but when he discovered that director John Cromwell was being replaced by Frank Borzage, he refused to do the picture. The part was then given to Gary Cooper.
Also: Ruth Chatterton, Claudette Colbert and Eleanor Boardman were announced to play the role of Catherine Barkley before Helen Hayes was cast. Boardman shot some scenes, which were all reshot, but some of her footage did make it into
The House That Shadows Built
(1931).

A rather bizarre movie I liked. He tried leaning back against walls and things of that nature but it was off putting. Strange actor matching as well. I don’t know what these casting directors have in mind when they make these decisions!

Haven't seen that one, but going by their IMDb bio info, Robbins is 6'-5", Morton in 5'-3", making for a 14" height discrepancy. Yes, that would be a similarly awkward visual pairing.

Code 46 had the same problem but even the angles didn’t help. When they panned out it was obvious Tim Robbins was a giant
and Samantha Morton was a midge.

In this film, it seemed pretty jarring in a few spots.

Yuck! I find that so not attractive.

Interesting. Thanks.

It was a year and a half ago, when I read the book and then watched the movie, so I have forgotten things somewhat, but from Wikipedia's plot summary we have:
https://en.wikipedia.org/wiki/A_Farewell_to_Arms
Not long afterwards, the Austro-Hungarians break through the Italian lines in the Battle of Caporetto, and the Italians retreat. The houses are evacuated. Women and children are loaded in trucks. At the villa, Frederic discovers that Rinaldi has taken off for the hospital; everyone else has evacuated too. There is considerable delay and chaos on the road during the retreat, and Frederic, wishing to avoid a possible aerial attack while stuck on the main retreat route, decides to take an alternate path. He and his men quickly get lost, and their cars are stuck in the mud, Frederic orders the two engineering sergeants riding with Bonello to help. Afraid of being overtaken by the enemy, they refuse and try to leave. Frederic draws his gun and shoots one of them; the other escapes. One of the drivers, Aymo, is later killed, while another, Bonello, runs away to surrender to the Austrians. Frederic and his last companion, Piani, catch up to the main retreat across the Tagliamento river. As soon as they cross the bridge, Frederic is taken by the military police to a place on the river bank where officers are being interrogated and executed for the "treachery" that supposedly led to the Italian defeat. Frederic escapes by jumping into the river. Afterwards, he walks through the plains and jumps aboard a moving train to Milan to find Catherine.
Of course, the Italian guards are shooting at Frederic as he jumps in the river. When he crawls out of the river, he has decided on a farewell to arms.

I thought the movie was pretty solid, and director Borzage certainly imbued it with some nice little directorial flourishes. That being said, I've never read the book, so at least I didn't have that to compare it to - and possibly detract from the viewing experience.

I guess such romances happen, but it might have been better with a taller woman.
My problem with this movie was that it doesn't following Hemmingway's book too well.
I guess from this comment from IMDB:
Ernest Hemingway hated this interpretation of his novel, as he felt it was overly romantic. That didn't stop him, however, from becoming lifelong friends with Gary Cooper, whom he met several years later. In fact, it was Hemingway who would insist that Cooper be cast in the lead of the adaptation of his novel For Whom the Bell Tolls (1943) 11 years later. However, the two made a point of never discussing this film.
that Hemmingway felt the same way.