(continuation)
In sentences 4 and 5, the omitted prefix is “pagka“, which may be used to give an “after (which)” meaning to a verb. For example:
Pagka-alis mo, matutulog ako. = After you leave, I will sleep. (alis = leave)
Pagkakain mo, magpahinga ka. = After eating/you have eaten, rest. (kain = eat)
Pagkatapos mong kumain, magpahinga ka. = After you have finished eating, rest.
Notice that in the last example, “pagka” was the prefix of “tapos”. The phrase “After you have finished eating” may also be stated as, “Then after eating”. It is in this sense that “tapos” in sentences 4 and 5 above get their “then after” or “and then” meaning. And again, you may replace the “tapos” with “pagkatapos” in those 2 sentences and their meanings won’t change.
When the prefixes are used, the accent on “pos” no longer applies and all the words containing “tapos” are pronounced evenly.