Where is it not working for you? I don't fly the A320, but my rule of thumb is 3 x the flight level as the start point, adjusted for wind. Eg, if at FL400, the latest I should be descending is 120 nm (3 x 40). Obviously, the FMS will have a 3 deg TOD point in it depending on the first constraint on the arrival. You can use this rule of thumb to help visualise if you're high or low.
My husband does fly the A320 and he has commented a few new guys get the speed way back to something like 220kt at 30 nm which then annoys the controllers and can upset the profile. Speed brakes aren't very effective when you're slow.
Checkboard You might be able to help here.