-t 4 -bits 55
1.0M j/s [runtime] 00:04:01
-t 16 -bits 55
3.2M j/s [runtime] 00:04:33

why are you

?
scaling depends on CPU, ie # of cores (typically 2,4,8 ... or 56 if you have a Intel® Xeon® Platinum 9282 Processor

)
and # of threads per core (which is one or two)
-t is generally equal to core number ... on some cpu's you might get better performance for -t equal to 2 x core number.