No sure if this helps...
But I find when ever the oil has been changed in either of our XT600e's the oil level always drops dramtically in the first 100km or so - not sure why this is, but I have come to accept it. I think the most I have added is one litre. After a service I always carry an extra litre of oil with me for a week or so, regularly checking the level.
However, on the plus side, once the oil is at the right level, it appears to stay there for ever.
As for warming up. I would echo Okrad comments. Ride the bike around for a good ten minutes and then leave it to settle in a vertical position for about 2 minutes or so, allowing the oil time to settle nicely, before checking.
Interesting, this dramatic drop in oil level is not something that a Yamaha dealer will tell you (warn) about either. Not sure they even know its an issue.