Whilst this would appear to have worked in this situation, Matty was absolutely correct to try and explain how the job should be fitted. Felt back vinyl is not a miracle product and is susceptible to bleed through of the flooring iunderneath as well as showing uneven areas if the subfloor is not level. A further option could possibly be to prep the floor with F-Ball Isolator, this is simple and quick to lay, then ANY vinyl could be laid over the top still allowing the floor to breath and resolving minor levelling issues. When you are selecting your vinyl, hold a sample up to the light, you will be able to see shadows through it easily, even with a felt back. A product called Imprezzo may be an answer if you can find a colour i their limited ranging, it's an LTV similar in quality to Karndean, Amtico and Camaro but it fits in It's own underlay system, well worth looking at the install vid on YouTube as its definitely a DIYable product if you fancy a challenge.