15.15.15.4 Over-constrain Placement for Routability

When Constrain routing is selected, an additional option to Over-constrain placement for routability becomes available. Selecting this option contracts or expands the size of a placement region, depending on the region's type. This usually creates a tighter placement region. For example, a normal MxN Inclusive placement region would shrink to (M-2)x(N-2). On the other hand, the prohibited region for external nets of Exclusive and Empty Region types would expand to (M+2)x(N+2).