Agreed. Generally about 6' high or a bit more works well unless you have a very low ceiling. Also, those types of speakers are technically designed to be directly beside the listening position so you're sitting in the null. However, with 2 rows of seating, this is a compromise for the 2nd row.
With 2 rows, they're generally mounted up high and between the rows so they're slightly behind the first row and not too far in front of the 2nd row.
This all assumes a 7.1 setup.
Bryan