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@gbj_tester
Do you mean a radial gap between the upper bearing ID and the steerer, or an axial gap between the top cover and the head tube?
If there's a radial clearance, the headset will still be wobbly, so I'm guessing you mean the latter
The gap between the top cover and the head tube should be about 0.1-0.2mm, but a bigger gap is mostly an aesthetic issue rather than a functional problem. As long as the headset is free turning and play free, you can live with a bigger gap until you find the ideal split collet.
The split collets are not a universal fit, some are taller than others; even though they have the same diameter and lead angle, there is often a short cylindrical part above the taper. This should be matched by the rebate in the top cap so that everything lines up (give or take a shim or two), it sounds like yours doesn't because you're mixing parts from two different headsets.