Set the "type" of recipe to "partial mash" and use the Single Infusion Mash profile. Adjusting from Light to Full bodied mashes as desired. The software takes a best guess into account because the malt profiles have "Yield Potential, SRM, or Color, and even IBU's for Extract's" settings assigned. Extracts will provide up to 50% of your yield, but actual efficiency depends on the same rules that All Grain does. Grain milling or crush, Water PH, Sparge temp, Number of Sparge Rounds, and Size of grain Bill. If it were me, I would make a base recipe with just the mini mash to find out what the SG is. Then steep it and find out how close you are. This would then tell you what your efficiency is. Hope this helps.
Cheers
Preston