An impurity seeding scan has been simulated in three different divertor configurations of MAST-U, showing the effect of the divertor geometry on the transition to detachment. The three configurations include a conventional short divertor, a Super-X divertorwith large poloidal flux expansion and a Super-X divertor with small poloidal flux expansion. Both Super-X configurations detach at the same impurity seeding rate, while the detachment threshold in the conventional divertor is much higher. A comparison of SOLPS results for all configurations is presented in a detaching plasma with target temperatures around 5 eV. The total power balance, the distribution of radiation and the divertor closure with respect to neutrals and impurities is analyzed.