If an ECART journal is required for a rounding difference, the journal will take the account and default dimensions from the Chart of Acccounts (GESCOA), misccellaneous accounts tab. If a default dimension is set on the account, this will be populated in the journal.
This can be overidden by setting a default dimension (GESCDE) - select CNVEC and then restrict by Company. In the required dimension type you can then select site or company.