The increasing penetration of converter-interfaced generation creates new opportunities for offshore wind farms to contribute to power system restoration. Grid-forming (GFM) control can enable offshore wind turbines to establish and regulate an islanded network; however, the proportion and electrical placement of GFM capability required for successful restoration remain important design considerations. This paper investigates the influence of GFM penetration and placement on the restoration capability of an HVAC-connected offshore wind farm comprising Type-4 wind turbines. A detailed time-domain simulation model is used in which an onshore GFM battery energy storage system initially energises the transmission infrastructure and offshore network. Following establishment of the first offshore GFM wind turbine group, the battery is disconnected and restoration proceeds using the offshore wind farm, with the remaining wind turbine groups progressively brought into operation using different combinations of GFM and grid-following control. GFM penetration levels from 25% to 100% are investigated, together with alternative electrical placements at selected penetration levels. Restoration performance is assessed using voltage and frequency deviations, rate of change of frequency, and active- and reactive-power responses. The results demonstrate that the proportion and distribution of GFM capability have a significant influence on the dynamic behaviour of the offshore island and show that full GFM conversion is not necessarily required to support wind-farm-led restoration. The study provides a framework for identifying suitable GFM penetration and placement for offshore wind power system restoration.