Conclusions

Things I've found:
I can't print with a raft. It's difficult to get off and blocks the ruler spot. Since I couldn't get the raft off I couldn't confirm whether or not the ruler spot was the right size, but the biggest one seemed right.
Secondly, the quarter inch by quarter inch surface seemed like it was not sufficient.
Next print: I went ahead with the ruler slot size from the third test and printed another attachment that was larger.