periodic trends - Variation in atomic sizes in the transition elements

From left to right across a period, effective nuclear charge increases in the transition series, just like in the p block, and so atomic size decreases. Here the electrons are being added to the d orbital, where shielding is relatively poor compared to the p orbital. It should follow that the increase in the effective nuclear charge is more significant for the transition elements than the p block in a given period, leading to greater size variation among successive members - but the size variation is smaller in the transition elements instead. In fact atomic size increases from Ni to Zn. Is there any logical explanation for the fact?