Reason for different sizes are the ligands they are doing the work against. Som ligands are more difficult than others. We try our best to size work units based on atom counts, however an additional complexities are how many torsions the ligands have and how well it matches up with the target. This will cause a variation in difficulty from one work unit to the next. Ligands are put in batches somewhat random, so we should have pretty even distribution between batches, but you may see differences between even two batches.

Thanks,
-Uplinger

Short answer: Nope :)

Thanks,
-Uplinger