A find or constrain found set should produce the same result, they are just different ways of manipulating your found set and your summary fields will display summary values from that found set IF your layout is based on the same table as the table in which you defined the summary field. If the layout is not based on that same table, different rules apply as to how the field calculates a summary value.
I suspect some other detail not yet described here is affecting the results that you expect to see. Please describe your layout and process in more detail.
I am using the summary fields in a calculation in an Insert Calculated Result script step for a field that isn't on the same layout as the table containing the summary fields. But when I do the initial find and get the records for the day, I get the correct calculation, but when I constrain that set the calculation doesn't change I get the same result as I did for the previous set.
I just put the summary field values in a local variable and changed to the layout where I needed to use them in the calculation