I have re-positioned the narrow top shelf, so that it is in the middle position now
On this shelf are two plants of "Maskotka", a bush / trailing variety, and the plan is for them to trail down from their lofty position. The height of those sticks is such that I can just close the lid of the coldframe if necessary.
Down below, positioned centrally, is one plant of "Losetto", another bush variety, but one which is supposed to benefit from staking. I'll not let it grow taller than the height of the shelf. "Losetto" has the added benefit of being very blight-resistant.
The fact that these plants will be effectively under cover even with the lid and doors of the coldframe open, will give some protection from the airborne spores of blight anyway.