One of Grover Ted Tate's stories was that if you did not fit into the capsule when it was open, you certainly would by the time it closed...
The need for the capsule was driven by an accident (one of many) in testing, obliquely referred to above. The test involved simulating the failure of an outboard engine at high Mach. The vertical stabilizer failed (yaw load + rudder load?) and the aircraft broke up. None of the crew survived due to the high ejection speed.