seiko and hp have a tool called a head positioning jig, it costs about $1000, what it does is hold the head straight and allows you to position front to back and slant.
What you are doing in essence is correct, but remember a little move goes a LOOOONG way.
go into your service menu and find head adjust 2-1 which is the mechanical adjust, it has crosshairs that you can line up, a little bit goes a long way. If you send me a PM I can see if we have a tech that is available in your area.