What's the reason for huge difference in memory footprint between Paper and Bowtie2 v2.4.2 ?

[Lilu-guo]

With 101bp length illumina sequences, Recorded in Paper's Supplementary Table1, the Peak memory footprint is 3.24 GB, both unpaired and paired. But in practical test using v2.4.2, the Peak memory footprint is 2.669GB for unpaired, and 3.234GB for paired.

Is it the difference of version, or am I using it wrong? Why it use more memory footprint for paired than unpaired?

[Lilu-guo]

Maybe I had found the answer, Offrate is default with 32, But actually 16 was used in Paper's test.