at the middle of vs in the middle of

Some examples from the web:

• There is, therefore, good reason to conclude that slightly soluble compounds (at the middle of this range) have similar carcinogenic properties.
• CM = percentage of cows' milk; 1 + = sample containing 1 % of cows' milk and spiked with pure bovine casein at the middle of the track.
• Each of them ate as fast as they could, edging their chair forward, and they met at the middle of the trencher.
• The QuickMask is now disabled. The selection occupies the right half part of the image (marching ants) because the limit of the selection is at the middle of the gradient.
• 1 + = sample containing 1 % of cows' milk and spiked with pure bovine casein at the middle of the track.
• And at the middle of this Levellers' paradise, Angelica Fanshawe, now Countess of Seacourt.
• Look at the middle of Discovery.
• All I need you to do... is just aim at the middle of the debris.
• We have covered a lot of tragedies, a lot of problems, a lot of conflict zones, a lot of hot spots in the region, because we were centered at the middle of it.
• So the clash of civilizations is here, and cartoons are at the middle of it?
• We have a shared center; we have a shared focus - that car stays at the middle of all our relationships.
• Put it at the middle of the street!
• I hope it's alright I'm being here, I mean it's at the middle of the night!
• The Ministry of Foreign Affairs issues the following ID cards to members of the staff of foreign representations. The coloured stripe at the middle of the ID card indicates the different categories:
• What is he doing at the middle of the road?

Some examples from the web:

• I'm in the middle of a case.
• I'm in the middle of a critical task here.
• You're right in the middle of this very unnecessary Venn diagram.
• I'm in the middle of a mystery.
• I got a call in the middle of a root canal.
• Perhaps death stopped his writing brush in the middle of a sentence.
• And in the middle of it there was a crowd of nightingales.
• We're in the middle of some pretty interesting stuff here.
• Sitting ducks in the middle of union square.
• We were in the middle of surgery and we all lost consciousness.
• It's in the middle of the building.
• Handel composed Scipione whilst in the middle of writing Alessandro.
• Description Beautiful paradise in the middle of Dalmatia.
• ABBOTT: Wombosi was assassinated in his house in the middle of Paris.
• I started to scream in the middle of the night.
• We're in the middle of a bachelorette crisis.
• I didn't want you in the middle of tonight's antihero protest.
• Look, we're in the middle of final prep here...
• They're in the middle of this economic meltdown.
• So I set up in the middle of the block.