My apologies, I see the issue now. Yes, looks like you will need to install Backdrops to ensure sufficient cover over the pipe, whilst maintaining a steady fall across the required line. I really wouldn't be tempted to try and lay the drain too steeply, I think it'll cause more issues than it solves, and could cause problems at the Treatment plant if incoming waste is arriving at a fair rate of knots and keeps stirring up what's already in there. It needs to settle during the first stage of treatment.
Rule of thumb dating from the Victorian Era for drain laying, 1:40 for 4", 1:60 for 6". You're aiming for a 'Self Cleansing Velocity', to ensure the water carries the solids along, and keeps the drain/sewer flowing. Too steep a fall and the water can race away, leaving the solid's behind, or launches them onto the benching opposite when it arrives at a chamber, or too shallow, the water trickles away, leaving the solids sitting in the pipe, both issues that could eventually build up and cause a blockage.
