Azure Host level metric v Guest level metric for available memory

Question

Hello,
I'm trying to understand why a few of our machines show very different "Memory available" metrics between the amount shown in "Virtual Machine host" and "Guest (classic)"
For example:
Virtual Machine Host - "Available Memory Bytes (preview)" avg shows available memory can dip to 200MB.
But Guest classic - "Memory available" avg over the same period is showing that the VM never dips below 10GB.
Its a Linux VM.
Can anyone explain why this is, and which metric I should be using as the one to look at?
Thanks