Personally I'd put it behind driver if you already have DD behind the passenger seat. Reason being, the capsule and baby weight combined can get quite heavy and turning, angling and lifting the capsule in and out with bub in it will get really difficult and be hard on your arms and tummy. If you have bad tummy muscles like me that'd be REALLY bad then. Also, if bub is right next to DD then there's the added temptation of touching, annoying bub etc. I have Elijah behind the driver and Oskar is behind passenger. It's good cos I can hand things to Oskar if I need to (if he's hungry or something) and if Elijah needs something I can get Oskar to hand it to him whereas it'd not work the other way cos I can't reach behind me when driving lol.