That is, if a horror movie has an opening weekend of x, ON AVERAGE you could multiply that number by the horror genre's internal multiplier to guess what he delist price after 4 weeks COULD be. I don't know what the average IM are exactly (people on these forums have data for this), but I do know that horror flicks usually have a smaller IM than, say, kids/animated films. Also, you an increase/decrease the IM by observing if the movie is frontloaded (people rushing to see it on OW/day) or not (frontloaded --> IM decrease). This is why big blockbusters usually have smaller IM (because the OW is genrally very frontloaded).
As an example, HSX uses 2.7 as the IM for every wide release OW (that is not a holiday or a long weekend). It would be advantageous to find data that shows which genres generally have larger and smaller IM's than this.
Hope this is what you were looking for.