WP, and other smoke shells, have an internal HE charge that splits the shell open. The WP is ejected through the pressurization from the internal explosion before the splitting. Also, the spin of the shell flings out the WP and splinters. It's probably true that the WP danger zone is greater than the explosive/fragments zone. That is, in the case of artillery falling at a steep angle. Certainly so for mortar rounds, that also fragment in this same way to release the smoke chemicals. The fragments would basically be driven into the ground. The explosive charge is about 1/10th of a normal HE shell. Many WP/Smoke shells use the HE shell bodies by the way.