The Central Rhombus

In a rectangle, the midpoint of two opposite sides are marked, and the corners of the rectangle are folded to meet the midpoint of the opposite side. This draws four lines, which mark out a rhombus in the centre.
Q1: Sometimes the rhombus is outside the confines of the rectangle. For which ratios does this happen? Q2: Under what conditions is the ratio of the diagonals of the rhombus the same as the ratio of the sides of the rectangle?