The accuracy of electronic design automation is increased by determining whether fill wires in a putative integrated circuit design should be effectively grounded or floating. For each signal wire in the putative design adjacent to the fill wires, a signal sensitivity value, which represents sensitivity of a given one of the plurality of signal wires to noise and timing, is determined. For each one of the fill wires, a fill sensitivity value is determined by: identifying coupling of each one of the fill wires to the adjacent signal wires; and calculating the fill sensitivity value as a combination of the signal sensitivity values of each of the adjacent signal wires for which the coupling has been identified. At least a portion of the fill wires are selectively effectively grounded based on the fill sensitivity value, to obtain a modified design.