Why is `ulimit` not limiting the memory usage as I expect?

Question

I am trying to limit the memory usage of a process

$ulimit -m 2
$/usr/bin/time -l ./myProcess arg1 arg2

The process run without being killed until time outputs

        7.00 real         4.83 user         2.16 sys
4154855424  maximum resident set size
         0  average shared memory size
         0  average unshared data size
         0  average unshared stack size
   1014384  page reclaims
         0  page faults
         0  swaps
         0  block input operations
         2  block output operations
         0  messages sent
         0  messages received
         0  signals received
         0  voluntary context switches
        15  involuntary context switches

showing that the limit has been overpassed despite the ulimit -m 5 command line. I have also tried the options -v and -l but none of them seem to actually limit the memory usage. I also tried with time to make sure it would not fail to see the memory usage of a subprocess. Here are all limits after using all -m, -v and -l

$ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
file size               (blocks, -f) unlimited
max locked memory       (kbytes, -l) 3
max memory size         (kbytes, -m) 2
open files                      (-n) 256
pipe size            (512 bytes, -p) 1
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 709
virtual memory          (kbytes, -v) 2

If I limit the CPU time (ulimit -t 3), then it works fine and kill the process after 3 seconds.

Question

Is there something I misunderstand about ulimit -m 5? Is there a bug in my ulimit version?

Is there an alternative to ulimit to limit time and memory usage of a process (not necessarily the bash session)?

Versions

I am on MAC OSX 10.11.6 and bash version 3.2.57.

Related post

The post "ulimit not limiting memory usage" is very related but I don't think the accepted answer offer any solution on how to solve the problem