Hi William,
Currently yes that is the way you would set your app up in order to pull the percentages based off of all of your closed tickets divided by all of your opened tickets. Summary reports summarize up all the data across records but they do not have the ability to run calculations off of the summary values displayed. Calculated columns in the report instead run the formula off of individual records, which means the math doesn't come out the same.
A relationship allows you to control how the data is aggregated before the math is done so you can control how you want it to all collect and then run the formulas on the summary fields. This then can give you a percentage based off something like a Type and Date combo.
