Won't what make what assymetrical? What do you mean?
And the decs are normally done on RS rows - they're easier to do and you can see what they look like. Besides it's the RS...
After you do the decs every row for 5 rows the next instruction is to dec every other row. So since you ended the decs on the RS, work a plain purl row and begin them on the RS. That puts the last dec row 'every other row' from the next one.
sue- knitting heretic