I'm not sure I know the reason exactly, but I do know that there have been several changes to the studio allocations recently (since the new schedule started this month).
So on weekdays Adele and Clara's shows now come from 82F.
Weekends Arielle and Jordan also now come from 82F. The chart comes from 82E and Danny is in 82B.
Interestingly, the 1Xtra breakfast show has been in 82D recently - it always used to be 82F.
It seems that any shows with a co-presenter must come from 82A or 82D as these studios are larger, making social distancing possible.