Robineg

Hi, I made a ship with Nuclear Lightbulb engine using liquid fuel, but the Isp in vacuum is only 700s. For this combination of engine and fuel Isp shoud be 1400s (0,8*22,136*Sqrt(6250)) as the formula in the part description says. But for some unknown reason, Propellant Isp modifier is only 0,400 and not 0,800. See the photo for details: https://imgur.com/a/PtPO4Qt Am I doing something wrong or is it a bug? I'm running KSP-IE 1.21.7.4 on 1.7.0.2483 KSP base game