As always, people underestimated the potential of a Horror movie. If it opens at $20m, it may have a shot at surpassing the total of the third movie, and I don’t even remember the last time that a fourth sequel, surpassed the previous one.
It also shows the consistency of the Insidious franchise, apart of the second movie (that was an isolated phenomenon), each movie of the franchise finished a bit above $50m.