When you say pastry, do you mean pie? Most flaky pastry, including flaky pie crust, needs a higher oven temp to set the layers so the butter won’t melt into the flour and destroy the layers.
If your pies are getting too brown before the fruit is done, then either your oven is too hot or you may have put too much filling in the pan. The best way to make a deep dish pie is to cook the filling stovetop and pour it into a fully blind baked crust.
Which shelf, for me, depends on the pan and the recipe and, if I’ve made it before, past experience. Often I find that I get the best pie crust if I start it on a stone, but then move it off after the first 20-30 minutes or so. In my oven, it seems like the stone transfers heat to whatever is on it, but then remains a little cooler for a long time. I confirmed this when making sequential pizzas.