You can’t really tell whether a main halyard is pulled up hard enough by wiggling the luff in your hand. The only certain way is to examine the sail once it’s set. A mainsail should have its centre of curvature (its maximum ‘camber’) just forward of halfway aft from the luff. A headsail’s should be about 35% of the way aft. This aspect of the shape of either sail is largely controlled by the halyard. More tension shifts the camber forward. Less allows it to pull aft. It’s common to find a roller headsail with inadequate tension. Look for wrinkles running across it from the luff as well as the general shape. For some sails, this may mean more tension on a windy day and less when the breeze is light. The only way to find out is to experiment.