Well, if you can prevent the original 13 colonies from giving up their land claims, then large states would become the norm. I think this could be done relatively easily with the southern states (Georgia keeping the northern parts of Mississippi and Alabama, North Carolina keeping Tennessee, Virginia keeping Kentuckey) the problem is that the northern states would have dificulty maintaining their claims because many of them were only disconnected claims that were really only on paper (Massachusettes claiming pieces of Michigan and Wisconsin and Connecticut claiming a thin strip of land stretching from northeastern Ohio all the way to the Mississippi to name two examples). They could probably keep them longer than they did in OTL, but they'll likely have to give them up eventually. When they do, they'll be admitted as less states because (a) thanks to the South, bigger states are considered normal and (b) since there are less southern states, there have to be less northern states in order to maintain the free-slave balance. Let's also say that Vermont is given to New York as compensation for giving up its western claim.
So we start with the original 13 states (7 free, 6 slave). Louisiana's admission brings it to 7-7. I'll say Louisiana sticks with the larger state trend by including most of Arkansas. Missouri (including the other part of Arkansas and probably some land further west) is balanced by a state called Ohio which may or may not bear a great resemblence to OTL Ohio (it's the Ohio/Indiana/Illionis one on my map. The rest of the Northwest Territory is admitted with Florida (east+west) as a balance. The Republic of Texas comes in as is with all its claims. This temporarily upsets the balance in favor of the slave states 10-9. The Mexican cession is divided into two territories, California and Deseret. California restores the balance when it demands to be admitted as a free state. Deseret becomes the spark that starts the Civil War. It was subject to popular sovreignty. The south secedes after it narrowly votes to become a free state. After that, the Oregon Territory becomes one state, and the rest of the great plains is one big state (called Dakota). So that's 23 states plus the Indian Territory (which has slightly different borders). If, due to butterfly genocide, we still end up with Alaska and Hawaii, that brings the total to 25. I know a lot of these states are REALLY REALLY big, but I figure that the land is sparsely populated, so they can get away with it. Keep in mind that Maine is still owned by Massachusettes here.