Top executives at New Hampshire's 23 nonprofit hospitals saw their pay increase by an average of 18 percent from 2006 to 2009, putting them in the middle of the pack when compared to their peers in other New England states, according to a report released Monday. The report by the New Hampshire Center for Public Policy Studies was requested by the attorney general's office, which had raised concerns about high CEO pay in 2010 when it rejected a proposed affiliation between the holding company for Catholic Medical Center in Manchester and the parent organization for Mary Hitchcock Memorial Hospital in Lebanon.