In recently purchasing both an Ignition insulation vest, but also the accompanying insulation jacket then I have been interested in keeping warm whilst enjoying a range of outdoor pursuits.
So, whilst I initially had some sizing issues [i.e. requiring on-line exchange of an XL to a L], the vest was quite warm and it kept my chest comfortable on a 10 degrees C day. In layering with a merino cycle jersey, and merino long sleeve t-shirt, then I found that my arms were cold and so perhaps I will try the jacket on my next ride.
Therefore, in considering the designer's challenge of meeting the markets requirement for the 'ideal size', I found the length of the vest a little longer than what I would have liked as when cycling I prefer a more streamlined profile and found that the fit might be improved by turning the bottom of the vest upwards, and inside.
Similarly, the design may also be improved by the installation of an elastic toggled drawstring so that perhaps you might make it a more of a snug fit around the waist to your individual requirements.
That said, I'm not really the build of an elite cyclist or perhaps a jockey, and so the fit I may prefer may be different to what others may like. At the end of the day the vest keeps you warm, and that is why I bought it.