Sheepskin rug in car seat

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I have read and understand the physics of the dangers of snowsuits or thick coats in car seats (or anything else thick between baby and the harness). A sheepskin seat liner UNDER the baby though - physics wise this doesn't seem to be a danger in the same way but am I missing something? Would it be a danger in a rear impact crash (but I understand these are generally less risky as tend to be much lower speed etc).
Basically our friends have given us their Cabriofix which also has a mothercare sheepskin seat liner in (probably this). It looks lovely and cosy for our winter baby but obviously I want it to be safe too. If there's any doubt though I'll just move it into the pram...

I'm sure it's fine. I can't find it now, but there was an online video done by a company that sells these sorts of blanket/liners and it was showing that a snowsuit was bad, but they then repeated the test with a liner and it made no difference to how tight they could get the harness.

Try strapping your baby in tight like you would then undo the harness without making it longer the put the baby back in if the harness is still as tight it will be ok if not then that how it would compress in an accident.

Babies get very hot in car seats and modern cars warm up really quickly Be careful your baby doesn't get to hot

Thanks for the advice. I'm confused about the compression thing because the usual direction of force (baby pushed forward against harness) wouldn't be affected by the liner. But maybe as the car comes to rest the baby bounces back and forward and then perhaps compression behind the baby would have an effect
I will leave the liner out for baby's first trip home from hospital and then test it out regarding harness tightness once we're home. If I can use the liner with the harness at the same tightness I think I'll be happy with it.