No, you are still trying to compare apples and oranges.
There is a six month mismatch between children starting school in Scotland where the cut-off is end of February and children starting school in England where the cut off is the end of August. P1 does not equal Reception. P2 does not equal Year 1.
All you need to worry about is that your child is in the correct year for her age, wherever she is being educated. Having completed reception in England may mean her literacy skills or numeracy skills are a bit ahead of some of her peers. But others will soon catch up and any decent P1 teacher will differentiate activities. (My oldest started school at 5.5 and could already read).
Putting her into P2 would mean that you have a 5 year old with children a lot older. 18 months older, who have already been in school a year, formed friendships. And it's unlikely that the school would agree to put her into P2 anyway, given her age.
When you return to England, she will again rejoin the class right for her age, as one of the youngest - unless you at that stage defer her (if this is even an option). Yes there might be things they have done ahead of her, but there will be things she has done ahead of the English kids. And she'll still only be 8.
Please please stop trying to compare two very different systems and using language like behind/ahead as that's just not right. Posting on Scotsnet might help too.