the gas springs don't need to go past centerline....only near it, unless you want them to actually keep the door closed in lieu of using a latch of some kind. What is the green object in your sketch ? Another spring? You won't need one there or the related bellcrank pushing on the upper link assembly.....the 2 gas springs on the lower links will suffice, as long as everything is tied together. Suggest making a angle-iron connector between the upper & lower arms (where they are shown in your sketch attached to the door) so that the door is adjustable in the vertical plane, but the geometry of the linkage stays the same. Also makes it easier to get final position.