Garden fence: on which side are the fence posts?

According to the installer, the fence panel is to be placed exactly on the property boundary and only the fence posts on the property of the selected neighbor

This is always how it is done according to the installer

Yes, then you just want it differently. Argument: Neighbor makes a hedge, I don’t want to look at posts. Legally, there is no difference. Except that the fence belongs to whoever owns the property where the posts stand. If the neighbor doesn’t care about that, I would ignore the 6cm and rather have security in the future.

so you would take the fence posts on your side so that legally you are on the safe side

Fence mesh on the boundary and posts also on our side

No, I would place the mat towards my side because of the appearance and because the neighbor wants to put up a hedge anyway, and the posts will either be placed on the boundary (or, if the installer absolutely doesn't want that) also on my side.

He means the two quoted factors that the colleagues apparently gathered from other threads belonged here in the opening post.

Exactly. Even without the usability deteriorations here, it would be a matter of netiquette not to let those giving advice have to piece together the needed information from the questioner's thread history. The facts belong on the table, not underneath.

What would you say, which option would you decide on (our current neighbors don't care)

Not only them, but you as well. Even without looking up possibly given information about the situation in your thread history, I can say one thing for sure: your joint crazy idea is a conceptless mess like no other. The fiddling with hedge and fence is nonsense in itself, even without further complications, i.e. ideally equal ground heights on both sides of the common boundary. A fence exactly on the boundary with a hedge next to it practically means that the axis of the hedge trunks recedes 25, better 30 cm from the boundary — has this consequence been considered? — abandon all hope that some symbolic foil sign will move the hedge to respect the fence! — in five years it will stand crooked like the seven of spades! Get behind a professional for a truly shared fence (the Schonimmerso installer is not the one). Simply banding together in an "Ismirdochegal" cartel is not suitable as a foundation for a peaceful common boundary. I assume the story of chain-link fence versus sweet pea bush is known, even if one is not a dedicated Raab viewer. Dreaming here of a happy coexistence of this one's hedge and that one's fence and thinking the only still decisive question is the orientation of the smooth and the post side shows that a whole battery of shots may not have been heard :-(

(or if the technician simply refuses)

Technicians have no desires. Technicians are performers, not decision-makers. It is wise to appreciate the experience of many clerks. However, this explicitly does not apply to those of the "always done it that way (without using their brain)" faction.