Hi All, 

I am in the process of creating a knit dress out of merino wool with a horizontal  stretch factor of about 80%. I am thinking of lining the dress with a silk charmeuse, which has a horizontal stretch factor of around 40.5%. My primary question is, what amount of negative ease should I add to the pattern, if any?  Based off the stretch factors, I assume that the wool by itself would require a small amount of negative ease to prevent sagging/over stretching, while the silk itself would do without any ease. I am struggling on how I can accommodate for both fabrics to achieve a form fitted knit dress that contours the body, without being too tight or sagging/over stretching. Then, my ultimate goal is to grade the pattern from a small to a medium and so my secondary question is, which stretch factor percentage should I use to obtain the conversion factor?  80 or 40.5?

If I were to guess the answer to both my questions, the wool would only be allowed to stretch to that of the silk lining. And so I would not use any ease in the pattern and  I would grade using the stretch factor 40.5. 

I will greatly appreciate help with either of my two questions. Thank you so much for your time in advanced!