why 4x8 is slower than 4x7 ?

d54a707b393fd8b5539b3d6f0573dcd5226a5214
4x8 meta1 ./scripts/development/run-argonnite-1.sh
73m45.983s

this commit
4x8 ./scripts/development/run-argonnite-4-7.sh
39m19.380s

Link: https://github.com/GeneAssembly/biosal/issues/323
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>