Welcome to the dark side MUWAHAhAhAh! Ok seriously I used blocks set on 16" by 16" patio blocks for years and never lost one because I lost a bunch...
I have to stack on less than ideal flat land and have found that when you have to stack multiple blocks like that, even when just two, it helps to take a few minutes, scratch the dirt flat where the blocks are going so the resulting pier ends up as vertical as you can ( without being terribly anal about it )