How much engine oil in the Regal Raptor DD250G-2N?

Hi guys, this is the follow-up of my recent post about my new RR DD250G-2N. As I got the bike new from the store, there was not enough engine oil in, less than minimum on the dipstick. I had to fill up 0.5 L. Now I made the first oil change. I did it by myself as I did not like to go to the Pubei Lu shop for such a small action. Besides this, I called the shop before and they did not have any 15W50 oil, just 15W40. The lady even said that 15W50 is worse. Ha ha, in this hot climate!

Anyway, I filled up 1.6 L as described in the instruction manual. Below minimum on the dipstick again! I measured the old oil. 2.1 L. That means the factory filled up 1.6 L, as I added 0.5 L later = 2.1 L. In this condition the level was in the middle between min and max. So, I just put the rest from the second bottle, 2 L in total. Now the level is at minimum.

The question is what’s wrong? Does the engine need 2.1 L or is the dipstick wrong? It looks like the dipstick fits to the casing as there is no space for deeper stick. Also the procedure described for measuring of the oil level is as in other bikes: Clean the stick and put it into the thread hole but don’t screw it in. When I was in the store after I added the missing oil last time, the mechanic there measured also in this way.

Does anybody have an idea what’s wrong?