No need to be at the same level of the very lowest part of the whole system / gear lever but suggested because if the position of the gearlinkage (which connects the gear lever with the small gear linkage / tie-bar) changes it may cause problems (gearlinkage may hit the ARB, cat, heatshield or the lift of the gearbox selector arm may be different which may cause difficulties in selecting reverse or 5th gear etc.)
Let's take apart the gear lever into two pieces: above the ball joint and under the ball joint.
1:If you lengthen the gearstick under the ball joint (but it's unvaried above the ball joint) the shift throw will be reduced (at the gearknob). In this situation if you shorten the gearstick above the ball joint the shift throw reduction will be higher.
2, If you shorten the gearstick above the ball joint (but no modify the lenght of the gearstick under the ball joint), the shift throw will be reduced. (this situation is in the CAD drawing because the OEM gear lever was used in the drawing).
The small gear linkage has similar effect: if you decrease the distance between its small ball and the bore of the gearlinkage connection, the shift throw will be reduced.
The angle may be different. It has no effect in shift throw reduction but you must pay attention for the movement of the reverse-lock sleeve bottom (because in the worst case you won't be able to select reverse). A wrong angle may cause an uncomfortable position in some gears. For example the gearknob will be too close to you in 2nd or 4th gear or on the other hand, it will be too far in 1st.
In this CAD drawing the angles are identical.
(The angle is important in that case if you lenghten the gear lever above the ball joint... may cause problems if the 5th is too far from me (uncomfortable - left hand drive). Now I'm using a 'Fast Road Shifter' (also designed by me) in my Williams which is lenghtened by 35 mm (compared to the genuine gear lever) but moves in the same throw lenght as the genuine one and the 'shift force' (the force to select gears) is easily adjustable in wide range from the driverseat. 2 pics:
I love it because the gearknob is closer to the steering wheel and does not move in a longer way and I can determine the shift force from sloppy/very easy to stiff(er).