improve speedup of large lattice

[CalCraven]

PR Summary:

A brief change in adding compounds to large lattices to give a slight speed-up, to align with previous PR #1107

PR Checklist

---

• [x] Includes appropriate unit test(s)
• [x] Appropriate docstring(s) are added/updated
• [x] Code is (approximately) PEP8 compliant
• [ ] Issue(s) raised/addressed?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 87.35%. Comparing base (19ce3b4) to head (38077cd). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1198 +/- ## ======================================= Coverage 87.35% 87.35% ======================================= Files 62 62 Lines 6586 6588 +2 ======================================= + Hits 5753 5755 +2 Misses 833 833 ```

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