I assume you are referring to RT Solos. In the Solo Window select "Custom" to select the number of complete bars over which to generate. There is no provision for leadins. Unlike with Midi Solos, you are unable to generate more than one RT solo on the Soloist track at a time, although the RealCharts for successive solos over a different range remain. To ensure that there is no abrupt ending for a musical phrase choose say an additional bar and then delete out what you don't need. Again you can repeat the generation until satisfied. If you use RealBand, then this will give you maximum flexibility.