Dolby Atmos vs DTS:X on a 5.1 system

[Hintermann]

I am restricted to a 5.1 surround system based around the Yamaha RX-V685 Receiver. After initial glitches it is now working pretty well but I am wondering about the best speakers setting while watching Blu Ray movies, especially those with Dolby Atmos or DTS:X audio.

I found that the system works extremely well all around with Atmos, with a good balance between spoken dialogue and action sounds. But with DTS:X, I have to jack-up the level of the centre speaker by 30% to achieve the same balance (and by 50% if it is DTS HD7.1 Master Audio). Am I doing something wrong or have others noticed this issue?