Slow vmotion/copy of VMs between 2 VMAXes

I am migrating VMs from 5.5 Cluster to 6.5 Cluster.  I am seeing problems when migrating VMS from VMAX 10K to VMAX 3 All Flash.  When I move/copy a VM to stay with in each storage array the performance is pretty good.  copying from VMFS 6 on VMAX3 to VMFS5 on VMAX10K is good, but when going from VMAX10K to VMAX3 can be very slow.  I do have an open ticket with VMWare and EMC.  VMWare think it a storage issue and EMC said storage is fine.   I see the DAVG in ESXTOP on the hba that has VMAX10K on it spike up to 30 and sometimes up to 60 when moving/copying between the 2 arrays.  Is the VAAI/Xcopy work when dealing with several arrays?

This is the behavior I have observed,  this is in a Vsphere 6.5 environment.

I find that copying and migrating from VMAX 10K VMFS5 to another LUN on the same VMAX 10K VMFS5 works as expected.

I find that copying and migrating from VMAX 3 VMFS6 to another LUN on the same VMAX 3 VMFS6 works as expected.

I find that copying and migrating from VMAX 3 VMFS6 to another LUN on the VMAX 10K VMFS5 works as expected.

I find that copying and migrating from VMAX 10K VMFS5 to another LUN on the VMAX 3 VMFS6  is typically works a lot slower.