Different gutters with susy sass

I have this susy settings:

$susy: (
  columns: 8,
  gutters: 1/4,  
  global-box-sizing: border-box,   
);

Sometimes I need different gutters instead 1/4.

See image for example:

And the code:

.wrap {  
  @include clearfix; 
  @include container (500px); 

  .box-1 {
    @include span(4 of 8);
  }
  .box-2 {
    @include span(4 of 8 last);
  }
  .box-3 {
    @include span(4 of 8 wide no-gutter);
  }
  .box-4 {
    @include span(4 of 8 last);
  }

  .box-5 {
    @include span(3.95 of 8 wide no-gutter);
  }

  .box-6 {
    @include span(4 of 8 last);
  }
}

I tried this without success:

@include span(4 of 8 wide (gutter-override: 2px));

I found a way to fix it but not if it is correct

@include span(3.95 of 8 wide no-gutter);

Thanks

You can change the layout like this

@include with-layout(12 1/8 fluid float after) {

  .box-5 {
    @include span(2 of 12);
  }

  .box-6 {
    @include span(10 of 12 last);
  }

}

Where the 1/8 is the gutter width.