Composite Datasets - Not Working

I've built a model in desktop using import and pushed the dataset up into service in order to use it as a golden dataset i.e. stop duplicating the dataset for dashboards. Building dashboards via directquery to this dataset works fine. However, changing the dataset is problematic due to it's size when making changes to the dataset. Therefore, I thought I would split the datamodel into two datasets and push them up to service so editing would be easier via desktop going forward. When I now create a composite model via directquery the visuals are failing (over 1m records error) despite the model and the relationships being identicle I dont get it, it's as if being a composite model it is less effiecient. See models:

Can anyone shed some light on why a visual using one attribute from broker and one attribute from policy would cause an error when they sit in two models joined as a composite? As shown the relationships etc are the same.

-UPDATE-

I've researched more and found the difference is that the composite model is using a cross source limited relationship. Anyone know how to solve this as it makes the composite approach a little pointless?