The reverse taper issue was discussed. Actually, the top soil has been washed away and it is down to the bare minimum. It was discussed that on the next repot, the soil level will be raised about 1 1/2 inches. What is deceiving is the size of this tree. This is not a large tree, maybe around 13 inches tall. So hiding that small reverse taper area is literally as easy as raising the soil level 1 1/2 inches.
I live in zone 7 which is not much different in temps than zone 9 and I have had a white pine grafted on black pine living happy for about three years.