About ETH mining speed on dual mode

While my 2x rx470 runs at 53mhs with ETH only mode, but around 48-52mhs with dual mode.
So, it's a bit lower than ETH only mode.
Anyone who's experiencing same problem? or, any advise?

Circumstance:
windows 10 pro
chrimson 16.6
claymore 9.1
saphhire nitro oc rx470 4gb

Config.txt:
-mode 0
-eres 4
-epool asia1.ethermine.org:4444
-asm 1
-dcri 8 # when with pascal
-dpool pasc-asia1.nanopool.org:15555
-dcoin pasc
-allpools 1

thanks.