A close examination on magnet wire tables of various manufacturers like `http://www.epicos.com/EPCompanyProfileWeb/Content/CABLES/Magnet%20Wire%20Data%20Sheet.pdf (page 9),shows that the ratio of the conductor area and insulation area it is not remains the same throughout the sizes of wires. Insulation building in thinner conductors, occupies more area compare with thicker one. For example the insulation of AWG #14 is 4% of the total diameter and 12% in AWG #30 (the second image it is exaggerated to show the impact).
The first question is: why there is not a constant ratio of the insulation area to the total area in all AWG conductors?
The second question is: can we take the advantage of the surface increase due to the insulation in thinner conductors and to design for more current capacity than thicker conductors?