Hippeastrums are Species and hybrids.
Hybrids have crossed so often that the seedling can have genetic throw back to any of its ancestors. So when you cross two hybrids the result may not be to your expectations, the seedlings will surprise you with the variation.
Crossing species have better chances of giving desired results.

Sown under the same conditions the seedling will vary in size, roughly the large, middle and the small ones. Some like to use terms, strong, average and weaklings.
Hens-Werner believes the weaklings should be destroyed as they will remain problematic; I feel that may be these are genetically small bulbs and may be even more pleasing.

Seedling of May 2013 sowing

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Below are two year old seedlings growing under same conditions, observe the difference in size of bulbs.
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This seedling of mine had two scapes but the size of bulb is about One and a half inches in diameter.

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Its pot on extreme left

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The siblings of seedlings illustrated in first picture were planted last year in separate beds. They are all growing well and maintain the same relationship in size. It would be interesting to see the result when they start blooming next year.
Arif