“The Book of Mormon” hit No. 1 on the Broadway charts last week — and it’s something of a miracle.Sure, Tony-sweeper “Mormon” ($1,455,329) has been sold out since last spring, and sky-high demand for tickets has pushed the average price paid per ducat into the stratosphere. But the show’s overall weekly tallies are limited by the size of its venue, the Eugene O’Neill Theater, which at less than 1,100 seats significantly hampers the gross potential when compared to, say, “Wicked,” the long-running hit in a theater of 1,800 seats. But last week, “Mormon,” undampened by a slow winter week that kept sales below par at many productions, improved on the prior frame, broke another house record and came out ahead of “Wicked” ($1,349,433), “Spider-Man: Turn Off the Dark” ($1,268,002) and “The Lion King” ($1,226,681). In a mark of the continuing demand for “Mormon,” its average ticket price hit $166. That’s way ahead of the second-highest per-ticket average logged for the week, $109, reported at Lincoln Center Theater’s hit play “War Horse” ($860,311). In one of the chilliest frames of Broadway’s annual winter slump, only a very few productions last week saw B.O. rise over the prior sesh, and the handful to do so — “Sister Act” ($482,863), “Seminar” ($380,701) and “Wit” ($244,728), in its first full week after opening — upticked only slightly. Despite all that, “Porgy and Bess” ($905,134) seems to have established itself as a solid performer in the face of the Street’s overall downward trend. It’s an open question whether sales will further rise along with the tourist tide later this spring. Overall sales fell $2.4 million to around $15 million for 23 shows on the board. The declines aren’t much of a surprise to legiters, who spend the year girding themselves for the tough times that hit the Main Stem after the holiday boom. Last year at this time, sales had slipped to around $12 million for 19 productions. Attendance also was down, by about 25,000 to 179,706. Still, that’s well ahead of the 145,000 theatergoers logged last year, and last week’s average capacity of 78% topped last year’s 73%. B.O. began to pick up this time last year. Whether the same will hold true over the coming weeks remains to be seen. The 17 musicals grossed $12,620,707 for 84% of the Broadway total, with attendance of 148,733 and an average paid admission of $84.85. The six plays grossed $2,404,123 for 16% of the Broadway total, with attendance of 30,973 and an average paid admission of $77.62.