First of all what you have is a true tartan. It is the prettiest tartan ever made, it is Cunningham.

Second when you taper the waist in the back you do lose the sett between the fell line and the waist. This is just part of making a kilt. With the number of pleats that you seem to have each pleat would only need to be very small and the effect would not be significant.

Wear that tartan with pride.