For the design of heat exchanger flanges and tubesheets, ASME and TEMA (like Taylor-Forge) provide a correction factor when the actual bolt spacing (circumferentially) exceeds the allowable bolt spacing. The correction factor is then multiplied by the moment to design a thicker flange. The use of this term is very standard in industry and is used in other pressure vessel design codes such as PD 5500 and EN 13445.
ASME Section VIII introduced the bolt space correction factor in the 2010 edition. This factor will be used in the design. The ASME code also states that for computing the rigidity index, flange moments without this correction factor should be used. If you do not want to use the factor, then check this box. This factor tries to accounts for any possible opening of the flange faces in the area between any two bolts. The default is to use the bolt space correction factor.