You might consider leaving them wild until you resolve the vertical trim and the side trim intersection approach.
I would look at other houses in your area that are of a similar vintage for clues to the way it once was.
I would make it a vertical cut with a back miter that then matched the trim running down the side of the house under the soffit (the frieze). This would join and lead your eye around rather than stopping it. Alternatively it could be a vertical cut that meets the corner trim (or pilaster as it can also be known as), again leading your eye to the next element in the building.
My four square had cedar shakes above the porch roof that ran around the entire upper story with trim above and below it but no corner trim. The shakes were countered/woven at the corner. Clapboard either met a vertical trim or often used a steel joiner that was lapped over and nailed onto the clapboard on each side of the corner (this was an innovation in the 20’s with the advent of kit houses and lower skilled laborers)
The vertical trim you are showing is based on the sad dimensions of vinyl parts or modern dimensional lumber choices at the big box stores.
I will find some pics of some of the kit houses of the era, Sears, Montgomery Wards and Aladdin all offered them and the images are good reference to how trim was dealt with during that era. There are also plan books from the time which would be appropriate reference (I own some of the catalogs from the era). I need to go to work early today so I can’t do so until this afternoon.
If you are interested in spending some time have a look at the teens to twenties versions of the Aladdin catalogues (a Michigan company):
https://www.cmich.edu/library/clark...y_City_Aladdin_Co/Catalogs/Pages/default.aspx
Great progress.