Shrinking pastry is one of those problems that feels random until you trace it back to a single decision made before the dough even touched the tin. The culprit is almost always insufficient resting time after rolling.
Gluten strands tighten when dough is worked. Rolling stretches them under tension, and if you line the tin immediately, that tension releases in the oven rather than on the bench. A minimum of 30 minutes in the fridge after rolling gives the gluten time to relax without heat forcing it to contract.
The second factor is how the dough is lifted into the tin. Pulling or stretching it to reach the edges introduces new tension. Instead, roll the dough loosely around the pin and unroll it over the tin, letting gravity do the placement. Press gently into corners without pulling the sides upward.
What the resting stage actually does
Cold temperature firms the fat, which holds the structure while gluten continues to relax. This is why chilling after lining matters just as much as chilling after rolling. Skipping either step produces the same result: a tart shell that climbs back up the sides during blind baking.
If your kitchen runs warm, extend each rest by 15 minutes. The dough will tell you when it is ready by feeling firm and slightly resistant, not soft and pliable.