That is correct: by general order from 1st Corps (Dutrch) Headquarters at Nivelles on 27 April 1815 the troops were ordered to line up in 2 ranks.

This decision was made right after the king, his sons and Wellington making an inspection tour of 2 days along the Netherlands troops. I believe it was initiated by the duke, who noticed the battalions were relatively small.

At the time corps still was commanded by Prince Frederik, his older brother the Prince of Orange only accepted command on 30 April and arrived the next day.