현재형 is narrative or descriptive. it has nothing to do with the result of the act. 과거형 emphasizes that the act is completed. for example 익숙하다 means you are familiar with something. 익숙했다 means you were familiar with something. and i think the example you just mentioned used the wrong verb. it should be 두 달 동안 한국어를 공부하는 후에 마침내 문장의 끝에 동사/형용사를 보기에 익숙해졌다. after learning Korean for two months i became accustomed to seeing the verb/adjective at the end of a sentence.