“The Book of Mormon” hit No. 1 on the Broadway top 10 last week — and it’s something of a miracle.Sure, Tony-sweeper “Mormon” ($1,455,329) has been a sold out hit 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 on the boards, 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,” average price paid per ticket hit a walloping $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 B.O. 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 running. Attendance also was down last week, falling by about 25,000 to 179,706. Still, that’s well ahead of the 145,000 theatergoers logged last year at this time, and last week’s average capacity of 78% came out ahead of the 73% posted in 2011. Last year it was around this time that B.O. began to pick up around town. Whether the same will hold true over the coming week remains to be seen.