Syntactic complexity has traditionally been measured by “macro-perspective measures,” which provide a paucity of angles from which to examine how learners actually elaborate a sentence. Mixing up a large variety of clauses with only “the number of clauses” or “subordination ratios” could lead to overlooking desired relationships between complexity and proficiency or task manipulation and linguistic performance. The current study attempted to capture the features of writing syntactically complex sentences through “micro-perspective measures,” such as clause types (main clauses, coordinate clauses, adverbial clauses, relative clauses, complement clauses, and non-finite clauses), and differences in learner proficiency levels. Participants were 28 Japanese EFL learners. Proficiency was operationalized via argumentative essay scores. To elicit syntactic knowledge, we offered the participants a specialized task that restricted the number of sentences in describing a plot consisting of six related illustrations. The results revealed that coordinate clauses, relative clauses, and non-finite clauses are more frequently produced in elaborating syntactic structures, irrespective of the writer’s proficiency level. Our findings also indicated that non-finite clauses are a more practical expedient for proficient learners than less proficient ones. Some pedagogical implications are also discussed.