Such as the picture I show.
Gap is important. It makes assembly easy. Normally we design gap1=0.1mm. Also gap2=0.1mm. Then RIB of front cover can inside easy and cannot loose. So, L2 is request for holding the RIB, we must at least have 1.0mm.
We design a step in Rear cover. It is design to cover the assembly gap. It Makes production more beautiful. Mostly we front cover is important face, so step1 is necessary. We usually design 0~0.1mm. you can’t see rear cover when you have a look in front. Another important thing, this DESIGN STEP must in Rear cover. Somewhere may get noise when you press cabinet if you have design it in Front cover. Finally we have the gap2=0.5mm at least. To avoid RIB intervene Rear Cover.
Radian is a usually design in structure. It makes RIB stronger and uneasy to crack.
A good design is most important in production. Experience comes from study.