"Every show in the same theater does NOT have the same potential gross. Rent had a potential gross of $768,979 around the time of its closing. Million Dollar Quarter, which played the same theater (Nederland) had a potential gross of $1,109,700. Newsies, which occupies the theater now, has a potential gross of $1,208,958. Three different potential grosses, three different shows, one single theater."
This is only due to ticket prices though.
Look, I'm not saying that the 50% of potential grosses thing isn't necessarily false but we could easily test this by someone posting the known weekly nut of shows and comparing.
FOLLIES was 625-650k, which had almost every factor that mjohnson2 listed including Star Casting, Large cast/Orchestra, a Revival yet was still over 100k less than the "50% indicator". To me this is not precise enough.
Give me claws and a hunch, just away from this bunch.