We develop an expression herein for the intensity scintillation index on a two-way (radar) path, in terms of the one-way index and the correlation between scintillations produced on the uplink and downlink. The expression is appropriate for monostatic (fully correlated) and bistatic (totally or partially uncorrelated, or anticorrelated) paths whose links are statistically similar and obey Nakagami m statistics. A companion expression for the mean apparent radar cross section (RCS) in the presence of scintillation describes enhancement on monostatic paths and energy-conserving depletion of mean apparent RCS on small-angle bistatic paths. The companion expression, which does not depend upon Nakagami m statistics nor require statistical similarity, is consistent with more detailed calculations by previous authors. Special cases of both expressions are consistent with recent monostatic measurements.