This area of the system is very complex and full of pesky calculations, dependent on the perfect management of the task fields that drive them. And yes, there is a disconnect between how these index values relate to the overall project progress status, which is driven from the combination of the projected dates and the critical path determined in Workfront.
Usage of these has several items to pay attention to…
Set project condition on the project to set to automatic instead of manual
Set up a perfect dependency tree across the tasks to ensure that the flags for critical path are set to most clean start to finish within the project
Set up each work task (no children) with perfect estimate on duration, planned hours, and assignments.
Set up each work task with perfect estimate for planned expenses, planned revenue, and planned user cost
Maintain the work tasks to start on time, finish on time, have hours entered for time of the schedule window, adjust percent complete when exactly needed, enter expenses values as planned, and mark correct status
And, I likely forgot one or two things in this list
Here are some support references to get into the details of this complex area
Project Condition
"https://support.workfront.com/hc/en-us/articles/217239547">https://support.workfront.com/hc/en-us/articles/217239547
SPI - schedule performance index
"https://support.workfront.com/hc/en-us/articles/216632068-Calculating-Schedule-Performance-Index-SPI-">https://support.workfront.com/hc/en-us/articles/216632068-Calculating-Schedule-Performance-Index-SPI-
CPI - cost performance index
"https://support.workfront.com/hc/en-us/articles/216632028-Calculating-Cost-Performance-Index-CPI-">https://support.workfront.com/hc/en-us/articles/216632028-Calculating-Cost-Performance-Index-CPI-
CSI - cost schedule index
"https://support.workfront.com/hc/en-us/articles/217182237-Calculating-Cost-Schedule-Performance-Index-CSI-">
https://support.workfront.com/hc/en-us/articles/217182237-Calculating-Cost-Schedule-Performance-Inde...
EAC - estimate to completion - based on hours or costs values
https://support.workfront.com/hc/en-us/articles/216632048-Calculating-Estimate-At-Completion-EAC- Doug Williams