Memory limit exceeded on every email sent

When sending the emails, BPGES always thinks it is exceeding the 2G memory limit. I logged the values for $current_memory in the memory_exceeded function, and memory_get_usage was consistently returning a higher memory usage than was shown by monitoring/logging system values. This causes the plugin to send the emails in batches of 1 email each, instead of a single batch including all the emails. We have filtered out the result for memory_exceeded and now all emails are being sent correctly, however I would like to know why memory_get_usage is returning such erratic numbers.