At the end, of Magical Girl Lyrical Nanoha A's and during Magical Girl Lyrical Nanoha StrikerS, Reinforce is quite small.
However, in the above image she is shown to be just as big as Vita. The image above doesn't look like fan art and it's obviously set a few years after StrikerS as Tina is wearing the Enforces' uniform and has longer hair.
I am wondering why Reinforce was so small. Is it because she was still a new born that's yet to grow? If so, can Agito eventually grow up to be normal size since both Rien and Agito are Unison Devices?