My memory is similar to tall guy. most of Holland was low level. From memory Amsterdam cleared us up the coats at not above 700ft or something similar. We ended up racing the cars at along the Zandvoort straight!
However further north there are a number of nature reserves and so heights have to be much greater. I would guess getting up that part of the coast at 4000 VFR is always going to be a bit of a lottery.