How do atomic sizes change from boron to thallium?

In the boron group (Group 13), atomic sizes generally increase as you move down the group from boron to thallium due to the addition of successive electron shells.12

However, this trend is influenced by the presence of filled inner d and f orbitals in the heavier elements—gallium, indium, and thallium. These inner orbitals do not shield the outermost electrons from the nuclear charge as effectively as the inner s and p electrons found in lighter elements. Because these outer electrons are not shielded well, they are pulled more strongly toward the nucleus, which results in the atoms of gallium, indium, and thallium being smaller than might otherwise be expected.1

Despite this effect, the overall trend remains an increase in atomic size down the group. The size of these atoms is a critical factor in determining their coordination number and the types of chemical compounds they form.123