The above calculator is available for your quick reference calculating.
A= length of the long tube.
B= Length of the 1/4 wave stub.
C= Feed point height above soldered joint
D= The spacing between the 2 tubes
For 2 meters the lower tube below the long one is 18 to 20 inches and I have found that this and the spacing between the 2 tubes are not critical.
The measurement is made from where the tube bottoms out inside the fittings and not from the top edge of the of the 90* or the *T* fittingJust go by the numbers on the calculator and you can't go wrong