You're doing well with catching boss fish, I've fished for 7 hours in total on this lake and only caught Oxen (carp), out of 234 fish.
It was much the same for me. The first boss first I caught was after a lot of fish. Oxlease Lake is more a challenge to fish but I prefer it like this. Its much better than catching 10 boss fish within the first hour! I like to explore different parts of the venue by moving around the pegs and trying a range of baits etc. By doing this I caught a few more bosses. Good luck and happy fishing!