What is the ratio of fat to flour in shortcrust pastry?

Typical ratios are 3:2 or 2:1 (flour to fat). In fact, you can use a flaky crust recipe if you prefer, the difference is only in the mixing. I have used these ratios successfully for short pie/tart crusts, both sweet and savory, and for different types of cookie. But I must note that the textbook "The professional pastry chef" uses 1:0.88 flour to fat, with 0.38 sugar and 0.11 eggs added, as the basic formula intended "as a base for cakes and pastries or to line tart pans [and to prepare] nothing-left-in-the-showcase cookies".

I haven't tried working with ratios outside the 3:2 to 2:1 range, but 1:4 strikes me as too buttery. It is probably not enough flour to hold together, you're more likely to end up with a stirrable roux base than a pastry crust. In fact, 1:1 is already a standard roux (although it might be a bit more pliable than stirrable if made with butter in an oven and then refrigerated).

If you meant it in the other direction, you can very likely make a crust with 4 parts flour to 1 part fat. Then it will be difficult to work all the flour into the fat, and you will have to add more water than with higher-fat ratios to get a cohesive ball. The more flour you add, the more you are leaving classic shortcrust territory and going into something else - something like a hardtack with a bit of fat.