Bernina's blog, WeAllSew offers four tips for creating better buttonholes, and the following tip for placing buttonholes on shirts and blouses.
When adding buttonholes to your shirts and blouses, avoid any “gaposis” down your front closure by aligning your first button at your bust line, and another at your stomach protrusion. Then space the remaining buttonholes accordingly. I personally like my buttonholes spaced no more than 2″ inches apart. It is okay, to choose the number of buttons you desire, not what the pattern suggests.
Click on the link above to view the tips for creating better buttonholes.