Our under ground vents were designed by our architect to sit externally a course below the finished internal floor height, and this is what was built. See attached drawing and picture. 
 

We are now onto the patio, and want our patio level to be the same as our finished internal floor, ie no step down, however if we do this we will block the vents! 
 

What is the solution? Our landscaper says the vents should be above the floor level. Our builder and architect say all new build under floor vents are positioned like this…

 

 

 

You could extend the vents out to the end of the patio with ducting? I'm going to do that but my air bricks are a few courses below yours so I'd imagine it's significantly easier. Depending on the patio you may need to use a telescopic to move it back down again... It's not a good detail by the architect sadly.