Baking – Which rack level of oven is suitable for baking choco lava cakes

Yes, there is a difference. You shouldn't be baking a cake (or anything else) in a microwave oven.

A microwave oven excites the water within your food. When you put in dough or batter, the excited water doesn't bind with the starch the way it does under normal heat, it escapes the starch, leaving you with a stone-hard piece of dough or batter.

There is something called "five-minutes microwave cake". I haven't tried it, but in the recipes floating around the interwebs it gets eaten while still hot (so probably before it has had the chance to get too hard). It also seems that there is a very small heat frame in which it gets OK. Bake it too much, and it will get hard, or burn. Bake it too little, and you end up with a mug of warm batter. It is also supposed to be a cupcake, I suspect that if you try to bake a bigger portion at once, there will be enough temperature difference in different zones of the batter to get underbaked, baked and hard portions all at once.

Bottom line: if you want to try for the fun of it, make a cupcake in the microwave, and watch your energy input (microwave watt setting and time) very closely, then eat immediately. You can find recipes all over the Web, e. g. on Instructables. If you want a real cake, don't bake in a microwave.

Mid height for cakes in non-convection ovens, slightly above mid height for thin cakes, top for cookies. In a convection oven it doesn't matter because the airflow distributes heat evenly throughout the oven's volume.