They have stated the same % will be getting the 4s, & 7s as in 2019.
That then means that the grade boundaries will be set accordingly, providing they stick to that.
if the cohort are at the same level, and the exams are the same difficulty then the boundaries will be more or less the same.
If the cohort is of general lower standard (which might still possibly be expected due to impact of covid) that would tend towards the boundaries being a bit lower.
But it also depends on how 'easy' the exams have been for the cohort compared with the 2019 exams. If for some reason they were easier and the cohort achieve higher marks, then the boundaries would move up.
Broadly speaking though, if you have a predicted grade 6 student who think the exams went about as they expected, then barring them having missed the point of a big mark question without realising, I reckon you could expect them to be in the same relative 'position' in the overall cohort and thus hopefully still be on for a 6.
In other words, no point worrying about it. 