This is a very common question that is asked by people who need to purchase DDA signs.
The Sign Design Guide (written by the JMU and the Sign Design Society) talks about ensuring a "consistency of location to help people find information when they need it". This is why we have developed our Braille finger push plate for doors; they relay Braille information in a location that is consistent and helpful for Braille readers: http://www.as-s.co.uk/braille-signs.htm
Please let me know any thoughts you might have.