BigMac,
Yep, the distance between hole-sets is about 4 - 5"...guesstimate, by eye. One of the reasons I went to the wider OD 4" drainage pipe is to allow closer spacing of these holes and still have a stable mass supporting them. One of the reasons I did NOT put them closer together was a trade-off on cost for the limbs. After seeing the sputnik sheres, I shifted gears to a less dense product knowing that it should still be suitable. You are right, though...you could surely put the limbs alot closer and denser if desired.
WRT pounding them into the bottom, I briefly consider that too, but dismissed it for the more stable 60# bucket design. Just a choice, but I felt it was worth the additional $4 per tree for long term stability.
