Antonyms for the phrase "more decent sized" include words such as small, tiny, little, mediocre, and insufficient. Small refers to something that is diminutive in size, while tiny is even smaller, often implying something minuscule or insignificantly small. Little suggests a degree of smallness that can be inadequate or insufficient. Mediocre implies that something is average, ordinary, or unremarkable in size. Finally, insufficient refers to something that is not enough, undersized, or inadequate for its intended purpose. These antonyms convey the opposite meaning to "more decent sized," which denotes something of a reasonable or appropriate size.