What does the cryptic crossword clue "Diminutive character good, the other half the size? (6)" mean?

The wordplay uses a charade (building blocks). G (synonym="G") + RUMPY (synonym="RUMPY") = GRUMPY The answer is GRUMPY.

Diminutive character good, the other half the size? (6)

Guardian Cryptic #29343 | 19 Down | 2024-03-29 flower