through a lot of explores and time I've found a some new information- there is a "biome of the day". What I mean by this is that every day a different biome will have all your hell hounds. yesterday for me it was the jungle, the day before it was the grasslands and today it was the desert. Send out two explores in each biome and then try a thrid if you haven't figured it out by then. Your biome of the day will give you 5/6 explores succesful generally and it should be a lot easier to get the hell drake. I hope this information is true and helpful- I've used it myself and I'm doing really well.
I've noticed something similar, but I stuck to random after I found a hound in a different map on the same day. Managed to get my drake yesterday, and my strategy was to use that wonderful item known as a Travelling Magician's Invite, several dozen energy flow cards, as well as exhausting my sanctuary and a lot of my pets, even the lower leveled ones. To be honest, it wasted a lot of potential resources from the islands, but I was in a rush for time. Just leave the islands without the hounds, and go after the ones that do in the shortest route. It netted me around 30 pumpkins within the day and a couple of doom pumpkins if I'm lucky with the temples, taking note of the energy regen timings.