Thanks for the write up. A couple of things that came to mind:
1) The number of packets for a day is limited because of the access policy, however the packets do not need to be distributed evenly over the 24 hour timespan to stay within the 30 second limit. The 11 packet worst case allowance could be used in 1 hour when no data is transmitted during the remainder of that day.
(This can cause issues if a significant number of nodes within reach of a gateway all choose the some time frame to consume their allowance)
2) A node that's close to a gateway at a certain point in time may not be close to a gateway at other times. This might be because the node is moving or because a gateway is down (for whatever reason). So its hard to predict what transmission speed is appropriate to reach any gateway. Using ADR could solve this (once TTN supports it) however this makes it harder to estimate what the 'save' amount of data and transmit interval is.