Trim tab, sorry, no sympathy from me.
Sometimes we are 2000 ft lower, worst I've had recently is 4000ft lower. But the direct routings that ATC provide more than make up for the level (especially from Maastricht!). And if you think about it, to guarantee your level, ATC would have to ensure that a 100nm section of your route is clear for you to climb into (15 min slot window at 400kt) Now that's just plain greedy, but if we went that way, nothing would move due to it's slot!
Min fuel is all very well, but you already know what happens and should ensure your fuel uplift is enough to cover your expected flight, not some theoretical dream...