In the detailed analysis wizard, you should click the SI Nets Spreadsheet button to specify which nets to simulate, and the thresholds to check in this simulation. Notice that the last column is for the maximum crosstalk.
Instead of declaring the threshold for all the parameters on all the nets, you can define a net rule and specify that to the associated nets. Click the Help button in the wizard for more information about defining and using net rules.
You can use the rule of thumb that crosstalk can use about 1/3 of your noise budget. Since this is a rule of thumb, you will hear a variety of answers to this question.