As a general rule for all tie knots, the widest part of your tie should hang roughly at the same height as the upper edge of your leather belt, with the tie's tip extending slightly below it. The tip of the narrow end would then hang wherever it may.
If you run into problems trying to get the length right with either the Windsor Knot or the Half Windsor Knot, try to let the wide end hang down as far as possible in step 1 of the instructions for these knots, so that when you cross the wide end over the narrow end, you can barely hold on to the narrow end. That will give you more length once you have eventually tied the knot.
However, it might also be the case that you are using regular length ties when extra-long ties might be a better choice. Use my extra-long ties calculator to see whether regular-length or extra-long ties would be the best fit for you.