Right now the pecking order has my Electric Indigo Dottyback as "top dog" and it totally intimidates the 6 line who is fairly small and measures about 1 inch
At an inch you have a fair chance of adding a halichoeres where it will be accepted by the sixline as they tend to mature into nasty fish but start out less aggressive. I personally think the starcki and dotty are more the issue at this stage but you will likely have real problems introducing anything in the future (they should all be fine together as they grow though).
If you do try adding something then an acclimation box is a good idea.