I am swapping out forks on my bike and cannot get this headset set right. The Grip Lock Cap won't go flush with the Upper Bearing Cup. I use this photo to show how it should be, mine has a gap. The fork will rock. What is a sure fire method on seating this? I had no trouble the first time I did this. Both forks are straight taper, nothing out of the ordinary. Thanks.

Do you have a gap so the steerer is 2-3 mm below the top of the stem or top spacer. If the steerer is too long, the top cap can't push the stem down to obtain the correct headset adjustment. You may need to add a spacer if that's the case. Also, did you loosen the stem's steerer clamp bolts before making the adjustment? They must be loose.

grip nut cap is for the threaded fork thats a threadless type.

Is the star-fangled nut supposed to close the gap? Stem is loose. The S-FN began to extract as I tightened, maybe I need to reseat/replace?

Do you have a carbon steerer? If so you must NOT use a star nut, you MUST use an expander plug. If it's a steel or aluminum steerer the star nut is ok. Either the expander or the star nut must be a tight fit and must not move as the top bolt is tightened.

... to piggyback on that, if you have a carbon steerer and an expander plug, play around with the location of the expander plug, I've found it can expand the OD of the carbon steerer just enough to make the headset parts not bed right. Try loosening up the expander, assembling the headset and stack and then tightening the expander and the headset.