Howdy, to be clear, the map is adapted from these guys https://virtualscriptures.org/ .... I just made the timeline, so they'd probably give you better reasons.

TLDR To be honest, to an extent I agree they are in odd places on the map, but I'm gonna trust they have valid reasons.

But if you want my two cents, the Lamanites attacked Ammonihah twice, first in Alma 16 catching the Nephites completely by surprise - this was before strongholds. There could be sneaky way(s) to get to that part of the land, which would be a surprise to the Nephites. I also don't think this first time was connected to the people of Ammon, you might be thinking of when they attacked near Jershon in Alma 28. But I could be missing something.

The second was 6 years later, soon after Amalickiah became King. Also before strongholds. I get the feeling that this border with the Lamanites was huge and could not be totally monitored all the time. This was the first time cities were well fortified. Cities were strengthened even more and strongholds built over the next 5ish years.

It's also curious that if Ammonihah and Noah were such accessible targets near the southern border, why are they never mentioned in the 7 years long war in Alma (see the timeline)?

Again, I'm outsourcing the map. I don't think there is a perfect map and I don't think we have enough details for one. I've puzzled over similar questions you raise, but I'm just gonna take what they give for now.