When polytonic Greek was abandoned, they for some reason chose to design the tonos (modern Greek, right in the image) different from the oxia (Ancient Greek, left in the image). In most fonts, there is verily no difference at all, but in some (I would assume those with a longer tradition, such as Garamond), the difference is quite pronounced; as demonstrated in ‘What is the difference between the accent on q and the accent on semicolon?’ (Latin SE), the Ancient Greek accents mirror each other, whilst the tonos has a steeper angle than the ancient oxia.
We have had a conversation in comments and chat on Latin SE, and although modern Greek is off-topic (on Latin SE), unless in relation to Ancient Greek, this question was deemed on-topic due to it concerning the transition from Ancient to Modern Greek. This question was therefore originally posted on Latin SE, and from the conversations in chat, I was recommended to crosspost this to a different SE that might be better qualified to answer my question. Though being on-topic on Latin SE, it is considered unlikely to get an answer, due to the question’s topic being on the side of the expertise found there.
Thus, my question is focused on the development from Ancient to modern Greek. I am especially considering the transition from Ancient to modern Greek grammar and typography, leading to the questions: Why are these symbols different from each other? How did the oxia develop into the tonos?