Elleste and Femoston contain different amounts of progestogen because they are different types of progestogen and are not directly comparable. They will require different amounts to do the same thing. Some are 'stronger' than others, and norithisterone is a particularly strong one, so you only need a small amount.
It could be that if you had continued on Elleste beyond 3 months, you would have had further side effects. I always found, when trying different contraceptive pills, that if you had difficult side effects, that you would be sure about it well within the 3 months, but it takes 6 months or longer to be aware of the more subtle ones. In fact it took me nearly 30 years to realise that lowering of libido was one of them.
Also, if your oestrogen levels have been low, you will feel the difference initially, then symptoms will return if the dose is not high enough.