change mainnav span

I have set up the mainnav to span9 with span3 items to the right. When it squeezes in for tablet and xtablet things overlap, so I was wanting to turn the span3 positions off and then turn them on above. I have that set up right, but I want to change the span of mainnav from span9 to span12.

I went to the ini and did this.

[mainnav]
position="mainnav"
default="span9"
xtablet="span12
tablet="span12

but it's not working. any ideas?