How To decide when to use one 2 foot tray versus two 1 foot trays in a letter presort in MailStream Plus

MailStream Plus follows the rules in the DMM when presorting a letter presort and filling 2 foot and 1 foot trays. 
Here is the DMM reference:
DMM 203.4.3.e
4.3 Letter Tray Preparation
Letter trays are prepared as follows:
e.  Mailers must use as few trays as possible without jeopardizing price eligibility. For instance, a mailer will never have two 1-foot trays to a single destination; instead, that mail must be placed in a single 2-foot tray. A 1-foot tray is prepared only if it is a full tray with no overflow; or if there is less than 1 foot of mail for that destination; or if the overflow from a full 2-foot tray is less than 1 foot of mail.
** Note:  These DMM rules are current as of Jan. 2017
UPDATED:  April 20, 2017