For each Paid SEM advertiser have them embed under a custom URL variable in your SEM account a custom ID. If you use Google and Bing for example. One for each. Then in all PAID search the IDs will be present. You then can filter on referrer contains the IDs or not including the ids, you could even do a Adobe Tracking ID for each as part of the custom variable. Then map users behaviour to organic vs paid via adobe IDs
if I understand your segment definition, you have 2 segment containers (1 visit container and 1 hit container) within the overall segment container. according to your results, I assume the "outer" segment container is scope "visit" as well?
you might face several problems:
1) visit container 1returning visits not matching conditions on the same hit natural search: basically the definition is looking for visits where they can find hits matching your definition. but: they do not need to be on the same hit, it is looking step by step. example: look at a visit, is there at least 1 hit matching condition "last touch channel" and at least 1 hit matching "server".... if it can find a visit matching all conditions somewhere, it will return the whole visit!
2) visit container 1 returning visits not matching "natural search": because you return the whole visit in container 1 it will even return hits where the user has another channel (before or after natural search in the same visit).
3) hits on the "excluded page": if your overall segment scope ("outer" container) has visit scope, it will return whole visits matching your criteria. that means it is looking for visits matching container 1 (see problems above) and combining with hits outside the desired page. so far so good, but of you have a visit segment on the "outer" container it will return the whole visit including the "pages from condition"
think this way: the condition defines "what to search for" and the container scope define "where to search for" AND "what to return".
maybe it is just enough to give "hit" scope to all containers and you might be fine...