They look pretty good.
When mushrooms are in higher light or flow than they want, they tend to remain small. When the lighting is lower, they will expand, to increase their surface area, this allows them to absorb more light. When the lighting is higher, they don't need to expand, as they are getting enough light, the way they are.
To try to get them to expand, you could try to put them in a low light, low flow area. But they do look healthy, as they are.