Joie iSpin 360 XL - room to recline?

Our LO is 8 months old but already growing out of 12-18 month clothes, as well as his small car seat.

We've bought a Joie iSpin 360 Signature XL with the aim of it lasting him for years to come, but keeping him rear facing as long as possible.

We've had an issue with the recline though - to be able to recline it basically at all whilst rear-facing, the seat in front has to be pretty much all the way forward. We often need to put him behind the driver's seat, so this is an issue. With the front seat back, the back of the baby's car seat is pushed upright - when he fell asleep in this position his chin slumped down on his chest.

We drive a Mazda 6 estate, so not a small car! Has anyone run into this problem? Or is it an issue with the fit? My partner removed all the inserts as we assumed they were for newborns - would replacing them help support him to keep his airway open when asleep?