Why is lithium iodide more covalent than lithium fluoride ?

Explain the following: (a) Lithium iodide is more covalent than lithium fluoride (b) Lattice enthalpy of LiF is maximum among all the alkali metal halides.

Lithium iodide is more covalent than lithium chloride due to

Lithium iodide is:

Why lithium halide is covalent in nature?