Is second cap > first cap ?

1st cap: large enough to avoid triggering the comparator under normal circumstances, you do not want too much ripple here.
2nd cap : large enough to keep the regulator happy for the time your program need run before the supervisor chip (mandatory with this method) reset the uC.
Both sizes depend on power consumption and time you need to execute the power down routine.

You may need to play with resistors around the comparator (any comparator appnote will tell you how) to avoid false triggerings.

Have fun,

Erik