Just changed over the coils on the T2 for the small 5inch one last night,over here in the UK most of the crops are in a advanced state of growth so untill the crops come off all i have is a fair amount of pasture,went out last night for a few hours and alsthough i was using a smallish coil still was not able to get down close to the ground as the grass is about 5inches high and 'wispy' so decided to change out for the small round coil and it was a good move.
This means that i can still carry on detecting till the crops are harvested,albeit i do loose a little depth and ground coverage but this small coil is like having a laser beam on a stick its that good.
It does pay to have a few extra coils as it gives you additional flexibility when detecting various ground conditions.