Hey Shawtay,
The way you wrote your first bullet point makes it sound like PoIs can be generated in any map field that is not blocked due to being unreachable or a house/GH. This is not how it is. Out of all map fields assigned to a certain discoverable subarea, some of them are in a black list which prevents PoIs to be generated on them. On the remaining map fields, a few of them are selected as "possible PoI fields". This is probably done by an algorithm the devs created especifically for this. Then, when the player clicks on the Discover button, a certain amount of those "possible PoI fields" are selected. This last selection takes into account the player's position.
Regarding your last point, the devs no longer "fix" unreachable PoIs. So, there is no point in reporting them anymore.