Hotels spend a lot of time crunching numbers and do get creative at times. In addition to calculating rates with minimum and maximum length of stay, they play games with "nightly" rates. Business hotels know weekends are tougher to sell than mid-week. When requesting a rate for a stay including a weekend night, some add up all the individual nightly rates and divide by the number of nights. Any change in start or end date will cause a new nightly rate to be appropriate. That's why some systems do not allow a simple "change", but cancel and rebook.

Separating reservations into likely segments will provide the least volatile rates.