One could argue that the Shannon Entropy in a new block will not in general be proportional to the size of the block, but that doesn't make any sense to me
I fear there's a misunderstanding here. The key point is the relation between the number of transactions and the size of the block (or the associated Shannon Entropy). With mechanisms like IBLT, the quantity of information transmitted on the wire (Shannon Entropy) is constant, whatever the number of transactions in the block.
I think there's enough contention on this topic that it deserves continued research. To me it seems fairly obvious (I could be wrong) that no scheme exists where simultaneously (a) miner's are free to build blocks according to their own volition, and (b) the quantity of information transmitted on the wire (during block solution propagation) is constant for all values of the block size Q. However, no one has proven this one way or the other so it's an open research question.
This looks great! I would love to go and present my paper.