Lennie's name certainly does not match in one way: He is a large man. However, it can be argued that it fits his mental capabilities. Certainly. the bulk and size of Lennie seem incongruous to his allowing himself to be ordered by such a little man as George. Yet, George definitely dominates Lennie, ordering him to do things.
As George lies on the sand with his hands crossed under his head, he complains that Lennie is
a lot of trouble....I could get along so easy and so nice if I didn't have you on my tail
Earlier he scolds Lennie and calls him "a crazy bastard" and other derogatory epithets. Yet, while Lennie is sent to fetch dead willow sticks, George hears splashings where Lennie has gone. "'Poor bastard,'" he said softly...," a comment that indicates sympathy rather than ridicule. Shortly after this, George goes into a long tirade about all the trouble Lennie is, complaining that he always wants what he cannot have. George says that he wishes he could put Lennie into a cage. Then, when he looks at Lennie, George's anger leaves him and he feels ashamed for what he has said.
Also in contrast to what George has said about how much better off he would be by himself, George explains to Lennie, "Guys like us...are the loneliest guys in the world....With us it anin't like that. we got a future. We got somebody to talk to that gives a damn about us."
I think Lennie's name would be considered an incongruity. After all, he is anything but small physically. Another incongruity is that George, who is described as a thin, small man, is obviously the boss of the two men. Lennie imitates hims and tries to please him. A third incongruity is that such a large man like Lennie would be interested in carrying a dead mouse with him. He is so physically powerful that a mouse would not seem to interest him.