On Mac OS X using eGPU RX 580 not using internal RX 570?

On Mac OS X Hascat recognises and is using allocatable eGPU RX 580 

But Hashcat is ignoring internal RX 570 pro card? It recognises it but skips it?

Also -  is it possible to allocate more of the GPU RAM to Hascat than the 1170 MB that it is using in this case?

The RX580 has 8GB RAM and the RX 570 has 4GB

Thanks!