I have the SMX-R's and they have an expansion gusset on the inside of the calf with a velcro adjustment section. Then they have the positive locking ski boot-type ratchet adjustment to lock them in place. The zipper only comes to the top of the ankle, the rest is adjustable. I don't have very big calves but have adjusted them for tucking in leathers over heavy socks before.
Find a dealer and try them on if you can, you should be OK.
If you have big calves, stay away from the Sidi line. I bought the Vertebra Airs and with my leathers tucked in, I could hardly get them zipped all the way up. I have them expanded on the rear as there are a pair of screws you can loosen and widen the boot a little.