A cross is not a "code" fitting. Therefore the piping codes do not offer any guidance on the SIF for this fitting. Therefore CAESAR II won't calculate an SIF and the software will warn you that it is using a 1.0 for the SIF value.

Here are two options:
1) Ask the vendor you purchase the cross from if they have performed any testing on this fitting and can provide you with the SIF values for stress analysis.

2) Model the fitting in an FEA package and compute the SIF numerically.

Anything else you do will be an assumption (guess) on your part, and hard to justify if there are problems with the system after it is in operation.