Have you read The Zulu War. With Colonel Pearson at Ekowe. By One Who Was There. published in Blackwood’s Edinburgh Magazine, No. DCCLXV, Volume CXXVI, July 1879 pages 1 - 29? Thought to be the work of the then Captain Edmund Leopold Clarke, (later Pelly-Clarke) 103rd (Royal Bombay Fusiliers) Regiment.
It is a fairly in-depth assessment of the siege. I have it as an original piece but the binding is very tight, making it awkward to copy.