“The Book of Mormon” stayed on Broadway’s top shelf last week, with the foul-mouthed Tony magnet maintaining its No. 1 slot on the Rialto.“Mormon” ($1,618,059) came out ahead of more frequent top dogs “The Lion King” ($1,599,094) and “Wicked” ($1,435,082) for the second week in a row. That feat was all the more impressive given the small size of the “Mormon” venue — 1,066 seats vs. 1,677 at “Lion King” and 1,809 at “Wicked”; demand for “Mormon” hasn’t flagged in the back-to-school weeks that have prompted dips at other shows. As mid-September frames go, last week wasn’t a bad one overall. Although sales still reflected the post-summer tourist slowdown when compared to the boom time of summer, box office was nonetheless up week-to-week at the majority of productions on the boards. A healthy five shows, including “Spider-Man: Turn Off the Dark” ($1,222,322) and “Evita” ($1,174,627), pulled in more than $1 million each. Contributing to the relatively strong September cume was the latter half of the fortnight-long Broadway Week, which encouraged attendance with two-for-one ticket deals at a slew of Rialto titles. Logging the biggest gain of the sesh was “Porgy and Bess” ($794,242), which saw sales jump 30% in a spike of last-minute biz prior to the show’s Sept. 23 closing. Also adding coin to the pot was Paul Rudd-Michael Shannon topliner “Grace,” with its first three previews pulling in $219,944, a plenty-respectable showing for an untried nonmusical title in the early days of its run. Also in previews, Manhattan Theater Club’s “An Enemy of the People” ($179,173) played its first full week while the Roundabout Theater Company’s “Cyrano de Bergerac” ($103,184) kicked off with five previews. New musical “Chaplin” ($460,925) was down a bit, but that’s likely attributable to the production’s heavily comped opening night Sept. 10. It remains to be seen whether the bio-musical can succeed despite the largely downbeat reviews last week. Overall Broadway sales rang in at $17.4 million for 22 shows on the boards, up about $475,000 from the prior frame. Attendance rose around 8,000 to 189,930 — an increase from the same week in 2011, when attendance came in at 178,675 for 20 shows that pulled in a total of $16 million.