there are a couple reasons you could fail the test, either the tab is not long/high enough to contact disconnector before striker crosses sear, or a new one I have discovered, possibly your sear is sticky, or has too little spring pressure and does not return fast enough. To check just the tab, remove receiver cover and do the same test, but in slo-mo with your hand, without the receiver cover off you will be able to see the sear pop up when carrier hits disconnector, it should be before the striker corsses the sear.
