I have flown 100' long x 7" diameter tube tails (over 2 pounds),
from many sport kites (Quantum Pro, Vented Katana, Vented Voodoo, etc)
I almost always connect the tail to the center-T area, not the keel tip.
That way, the load goes almost directly into the bridle and the kite
doesn't feel any of the stress.
Friday night (winds gusting near 30 mph)
There is much more stress on the kite from the high speed, high wind turns than the tail would ever produce. Just look at the inside leading edge.