Python multiprocessing: chunksize parameter not respected, always sends 1 item

After reading @Darkonaut 's answer here I am still having trouble getting batches of my iterable sent to the function to be multiprocessed.

My set up:

$ python --version
Python 3.6.7 :: Anaconda, Inc.
OS X 10.15.7
Also tested on RHEL 8, same result.

Here is a minimal example with the output below

import multiprocessing
from itertools import repeat

iterable = list(range(1000))

def dummy_func(arg1, arg2):
    if hasattr( arg1, "__len__"):
        print(f"Batch size: {len(arg1)}")
    else:
        print("Single item sent to func.")

    print(f"Arg1: {arg1}, Arg2: {arg2}")

with multiprocessing.Pool(processes=8) as pool:
    pool.starmap(
        dummy_func, 
        zip(
            iterable, 
            repeat("Static second variable")),
        chunksize = 10)
    pool.close()
    pool.join()

No matter if chunksize is None, or any number above 1, it aways sends a single item. Output:

Single item sent to func.
Arg1: 0, Arg2: Static second variable
Single item sent to func.
Arg1: 1, Arg2: Static second variable
Single item sent to func.
Arg1: 2, Arg2: Static second variable
...
Arg1: 989, Arg2: Static second variable

My expectation was that arg1 would be a list of items of length chunksize, is that not correct?