Clarify peak b field error message

[athoynilimanew]

Description

closes #4467

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.88%. Comparing base (b47db55) to head (6958af7).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4580   +/-   ##
=======================================
  Coverage   49.88%   49.88%           
=======================================
  Files         151      151           
  Lines       29871    29871           
=======================================
  Hits        14901    14901           
  Misses      14970    14970           

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