I created a project box and have printed it before. I increased the height to 75mm but it added a top cover when it was totally open. It does not show up in the slice image. Its a simple 4 sided open project box with square corners and 10mmx10mm corners with holes for inserts. The bottom has standoffs. Everything printed fine up to the top 5mm where it started printing a top layer. What can I try on my settings?