Memory Size Discrepancies between machines

I have a handful of virtual machines I created years ago as Linux A0 machines. A0 machines are described as having 750 MB of memory. These are now considered "Classic" virtual machines. They have been humming along nicely with their workload.

I recently created a few more virtual Linux A0 machines with the same specs for the same purpose. They have been struggling with their workload.

Checking "top" on the classics shows KiB Mem of 740,000 total. Checking "top" on the new machines shows KiB Mem of 660,000 total and a lot of time dedicated to the process kswapd0 for memory management.

Is there a way to allocate more memory for these new machines? I would think a machine created with 750 MB should report that it has close to that available. Thank you!