well a point source will throw a hard shadow - so the smaller the point the sharper the shadow.
As for shadow size on a background wall, you can figure out where/what angle - it's trigonometry. For simplicity sake, let's pretend the light source is completely flush with the floor. There are literally infinite places to stick a light to get a "comically huge" shadow - so let's hold some values constant for the example.
Let's say you want to throw a noir shadow of an actor on a wall. Your actor is 6' tall. And you want the shadow to be 12' high (6' above head-level). Let's pretend you can cut into your floor and put a point-source light at floor level exactly. So to figure out where to place the light, trace from the top of the shadow where you want it to be (we said 12' high) to the top of the actor to the floor. That point will be 12' away from the wall. You've made a 45-45-90 triangle - the legs of the triangle are equal. Bringing the light closer (still on the floor) makes the shadow bigger. Raising the light from the floor will make the shadow lower (but not technically smaller).
So for a shortcut - start with the light 2x as far from the wall as the object is. That'll give you a shadow 2x as tall as the object - though the light must be even with the base of the object to see it "head to toe" and double height.