I believe the current standard is 8 pieces of terrain, two of which block LoS. The ITC has added that all of the lowest levels of Ruins always block LoS. This has caused some problems where things like Night Spinners, Basilisks and Wyverns are OP...The bonuses from Vigilus make the problem even worse.We definitely did have that problem until we started using a lot more terrain.
Also, define 'we'. How many tables are you running simultaneously? Do they all have the same amount of terrain?