Cowpats at Knepp are deposited by longhorn cattle which are run to organic standards and are largely self-medicating - whereas conventional modern farm cowpats are stuffed full of antibiotics and powerful wormers which kill invertebrates, and are effectively chemical rather than biological entities. The Emperor has taste.
Numbers continue to remain modest, with Emperors only intermittently active due to periods of cloud. Also, and crucially, from working the unusually open habitats at Knepp it has become clear that Emperors avoid windswept territories and sallow thickets, and are effectively wind-distributed - look leeward for them.
Here's an unusual photo of a male on bramble (it was a random landing late in the day) -