Don't waste good caulk by pouring it into a large gap. For gaps larger than 1/4", first use a foam backer-rod to fill the space.
The hourglass shape of the caulk bead when used with a back-rod will stretch to withstand joint movement better than any other configuration.
a bathtub, first fill the tub with water. The weight will pull the tub downward, maximizing the size of the joint. Apply a flexible, waterproof caulking along the edge of the tub in full contact with both vertical and horizontal surfaces. This prevents future stress and cracking of the caulk joint. EHT