Why Tallboy was ill-suited to island strongpoints

How effective would Tallboy or Grand Slam bombs have been against heavily dug-in Pacific island defenses?

Devastating on a direct hit, but generally an inefficient use of explosive because small tactical positions were too difficult to identify and hit accurately.

The weapon is characterized as effective against large strategic point targets rather than small tactical positions on Peleliu or Iwo Jima. It needed sufficient release height to build penetrating momentum and a target visible early enough for the bomber to line up. Reliable tactical use would require later guidance technologies such as television, laser, or highly accurate satellite navigation.