Previous posters have written
- "...plus a tiny bit extra due to the climb vector", and
- "Since the glider is being towed uphill, the load is slightly more."

Actually the load due to being pulled uphill is typically 10% of the
weight of the glider (thinking of a typical climb of 6kts at 60kts
airspeed).
This is significantly larger than the drag component, which is in the
range 2.5% to 2% for a decent performance glider (say L/D of 40
to 50), and maybe 3.5% for an old 2-seater (L/D of 28).

Pedantry?