I think you are probably a bit confused here, for now and as far as I know it is not possible to boot stock horizon (what you call ofw) under an emuMMC partition. So the first partition of your SD does not contain your ofw, it just acts as the regular sd card you put on your switch, and the ofw is actually on your sysNAND. The second partition contains your emuMMC, that you boot under cfw, if I understand correctly.
Be careful though, if you update your sysNAND through the official firmware update autoRCM will be disabled and your fuses will be burnt upon restarting your switch. For now the only way to update your sysNAND without burning fuses is to temporarily boot it under CFW and update through ChoiDuJourNX, but if you're not careful you take the risk of getting banned, especially if you don't have a european account where you can disable telemetry.