Car seat straps leave marks by ds neck if he falls asleep in it

[Inspirachion]

It's new, a britax duo, ds seems very happy in it after vocally hating his previous rear facing for ever!
However I'm not sure if the red marks by his neck when hes been sleeping suggest it's not fitting him properley - he's the correct age and weight and I bought it from qualified fitter 3 weeks ago. Thinking of taking it back. It's not normal for this to happen is it?

Are the straps too tight?

Are the straps coming from below his shoulders instead of at or above?

Do the red marks happen when he is not sleeping i.e. is he reacting to the straps (flame retardants?) or are they pressure marks/friction marks if he is restless when sleeping?

Would something like this help?

does it fit correctly over his shoulders? Sounds like the straps might be too high up - the slots that the straps go into should be level with the top of his shoulders, not above or below.

Do you have shoulder pads on the harness straps???? If not, you should get some. They are a safety device. If you do have shoulder pads on then that´s unlikely to be the problem.

Thanks everyone. Had a really good look again this morning. He is generally happy iin the seat, straps are snug but not too tight. It's a pressure mark rather than a rash ( reaction to fabric etc). As I drive back to the shop he fell asleep so they were able to look at the problem for me. I think the way the pads fit over the straps is designed for taller child tho hes correct age and weight. Assistant said they will contact manufacturer for advice or swap for another brand - I'm waiting on them calling me back. Thinking maybe get it refunded and go for one if the kiddy ones with cushion instead but shop does not stock those. Don't know if they will refund me.