By combining all three tests you get 91-95% on three tests at the 0.08 level (DWI Detection and Standardized Field Sobriety Testing Student Manual, VII-5) but were inconsistent still leaving a significant false-positive result.
It is necessary to emphasize this validation applies only when:
a. The tests are administered in the prescribed, standardized manner.
b. The standardized clues are used to asses the suspect’s performance.
c. The standardized criteria are employed to interpret that performance.
If any one f the standardized field sobriety test elements is changed, the validity is compromised. (DWI Detection and Standardized Field Sobriety Testing, February, 2006 Edition).