I have noticed when one forms a more complicated sentence, that the helper verb seems to either go prior to the last 2 verbs, or at the very end of the sentence. These examples may help clarify what I mean:
weil ich ihn aus dem Haus kommen sehen KONNTE
dass er von ihr gesehen worden sein SOLL
nachdem ich ihm aufräumen geholfen habe
versus:
obwohl du uns HÄTTEST helfen sollen
nachdem sie uns nicht HABEN einladen wollen
bevor du das Glas HAST fallen lassen
How do you know when you put the helper modal verb prior to the final verbs vs. when you put the verb right at the end?
Explanations would be much appreciated - I've tried to figure out a pattern but I've been really struggling to see what the difference between the two differing structures are.