Rear wall panel position & sliding doors

Hi, Is it advisable to always install panels, be it diffusion or absorption flush to the wall or would a 3-4inch gap be ok? I've a tricky rear door situation that would be solved with a sliding door but it would mean the door needs to slide where my rear wall panels will be. If I could install the panels 3-4inches out from the wall that would solve the door issue as long as it doesn't negatively affect the panel effectiveness (this is an inner door, there is a small sound lock with another door outside this, both are 1hr fire doors being acoustically treated. Room is fully floating, room within a room construction, inner shell is currently 3.85m x 2.76m x 3.15m (LxWxH) Thanks

Generally a gap between absorption and boundary boosts LF performance.