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Tony, the white paper technique just gets you close enough to make collimation quick. Not to worry though, it is just a tip. I would be a bit concerned though about not seeing concentric circles. I have not seen this before and have owned a lot of SCT's and helped people sort their collimation out. I have no doubt this does happen, although I would not accept a scope that performed in this manner as the scope is limited by the alignment.
One of one, glad to hear you got your collimation sorted. Increasing the power will give greater collimation and will help each time you setup. Only high level collimation will give you the superb views these scopes can produce. Only on rare nights of excellent seeing (ie 8.5/10 +) can you use the slight tweeks with a focused star. You can then see the airy disk without it being distorted by the seeing. In average to good seeing, it is not advisable to used the focus star technique for collimating an SCT.
Anyway, let us know if we can be of more assistance.
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