There was an FAQ for this on the previous versions - it is a tradeoff when you use any higher detail mesh software - such as VFR scenery.
At some airports I notice that the airport is on a raised plateau, yet in real life it is not – why is this?
In this case it means that the airport in real life is not on flat even ground but probably situated on a slope. Flight simulator has to ‘flatten’ and even out the level of the airport to allow the AI traffic to operate correctly. It raises the lowest part of the airport to be level with the highest part of the airport and gives the airport a plateau effect around the lowest part. In real life some airports may have as much as 100 feet difference within the airport area. In Flight Simulator the flattening effect has to cover not just the runways and taxiways but also the entire area of the airport. The default terrain in Flight Simulator in the UK is at fairly low detail and so normally this flattening is not noticeable. When the terrain detail is increased greatly, as with the terrain included with VFR Real Scenery, then it can make it stand out. If you find this too distracting then you can turn off the high detail terrain and revert to the default low detail although of course this will also lose the high detail terrain over the whole VFR area.