One consideration for promotion is based on yr readiness to take on jobs at a higher level.

EP is a measurement of where u will eventually reach before your retirement. Performance grade is NOT the sole indicator (esp. when nowadays ranking is relative). What drives yr CEP is how well you perform in the responsibilities given to you, and the impact u have made, both within dept, across level / sch-wide. If you're GEO 2 / GEO 3, T&L should always be the main focus. Once you hit GEO 4 and above, mentoring / developing others professionally will come into play. Hence the bulk of C- & Ds will usually be from these sub-grades, because some got promoted way too fast and they are not able to meet the demands / KRAs at a higher sub-grade.