with the smaller plants they tend to get less light and have a small root mass so they need to be watered less often than the bigger plants
this is where a lot of growers mess up, they water all the plants at the same time so the small plants are getting over water often, this stunts the growth
best thing to do is lift the plant up so the plant canopy is 1-2" above the rest, give it the best spot directly under the light and only water her when the soil is nearly dry, this will give her the boast she needs