correct the chunk size by adding header size

[dangthatsright]

What does this PR do?

Fixes #393

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in GitHub issues there's a high chance it will not be merged.

Did you have fun?

thanks @tchaton for the help!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72%. Comparing base (b9aa903) to head (af5db07).
Report is 1 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (b9aa903) and HEAD (af5db07). Click for more details.

HEAD has 12 uploads less than BASE

Flag	BASE (b9aa903)	HEAD (af5db07)
unittests	6	2
3.10	3	1
3.9	3	1
ubuntu-22.04	2	0
macos-13	2	0

Additional details and impacted files

@@         Coverage Diff          @@
##           main   #394    +/-   ##
====================================
- Coverage    78%    72%    -7%     
====================================
  Files        34     34            
  Lines      5037   5039     +2     
====================================
- Hits       3941   3607   -334     
- Misses     1096   1432   +336     

[bhimrazy]

Closing this PR as issue #393 has been resolved by #395.

Thank you @dangthatsright for taking the time to raise this issue and work on it.
We encourage you to test it with the latest updates from the main branch,
and we welcome any feedback on how it goes.