The turning radius R is given by,
$R \ = \frac{V^{2}}{11.26 \ tan \theta}$
where,
V is the true airspeed in knots
R is turning radius in feet and
θ is the bank angle in degrees
If the glider is turning at a radius greater than the tow plane, i.e. it is in the outside of the turn, it must be flying at a higher speed in order to complete each circle in the same time. For glider in the inside turn, the opposite is true i.e. the glider is flying at lower speed compared the tow plane.

Image from FAA Glider Flying Handbook
Also for outside turn, the bank angle of the glider should be higher than the tow aircraft to compensate for the higher speed. The reverse is true
for an inside turn.

Image from FAA Glider Flying Handbook
Therefore, the only way the two aircraft can fly coordinated with the same bank angle is if they have the same speed and turning radius.
Flying the glider in inside of a turn is preferred because it is easy to give corrections (to have same speed and turning radius) compared to outside turn. The glider bank angle can be reduced till it returns to the correct position. Since the glider is flying at a lower airspeed (than the tow plane) it will accelerate as its turn radius increases so there will be no tendency for slack to develop in the tow line.
For gliders in outside turn, the bank angle has to be increased to reduce the turn radius. However, as the glider is flying faster compared to the tow plane, it (glider) will tend to overtake it as turn radius is reduced, developing slack in the line unless airspeed is also reduced (usually by yawing the glider away from the towplane). In this case, the correction process is more difficult.
For this reason, it is advisable to
...match the tow plane bank angle and point the nose of the glider at the tow plane's outer wing tip.
at-least for small bank angles.
In general, it is better to be in the inside of turn rather than outside:
If you have to err on one side or the other, it is better to err on the inside – especially when at a low altitude. This way, you’re not in as much danger of locking out.
as long as you are not too far inside so as to sink and stall.