Their are very specific dimensions in order for your Safety shower to comply with AS4775 Emergency Eye Wash & Shower Equipment:
Below is an excerpt from AS4775 as it relates to the height of the Shower head.
Section 6 Page: 6
Plumbed & Self-Contained Emergency Showers:
Section: 6.2 Performance of Shower Head
Emergency Showers shall be designed and located so that the bottom of the shower head is not less than 2083mm nor more than 2438mm in height from the surface on which the user stands.
The spray pattern shall have a minimum diameter of 508mm at 1524mm above the surface on which the user stands, and the centre of the spray pattern shall be located at least 406mm from any obstruction. The flushing fluid shall be substantially dispersed throughout the pattern.