On my wife's hybrid. it's about 4" from ground to pedal axle center and it's about 6" from ground to the pedal axle center of the stoker crank of our recumbent tandem. (Captain's crank is much higher on this bike.)
What kind of tandem do you have and are the wheels the original size? Stock crank size/s?
Pedal/ground strikes should be rare events and easily avoided.
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Bacchetta Giro A20, RANS V-Rex, RANS Screamer