I am looking at Emlid Flow right now. I am assuming you are using a projected state plane for your horizontal and then using NAVD88 for your vertical system.
On my Emlid Flow whan choosing a state plane system, NAVD88(GEOID18) is one of my choices and it does not give an EPSG code for the vertical but does for the horizontal system. I did have to download the tif file with the undulation grid the first time I used it.
Are you on different firmware maybe? I haven't fired up my Emlids in a month or so.
Yes, 6360 is NAVD88 US ft.
On my Emlid Flow it has you choose both your horizontal and vertical systems and then choose if they are in US ft, ft or meters.
Are you still using Drone Deploy? In my opinion, it makes it harder to use vertical systems since it doesn't use geoid undulation grids and works more like Pix4D with an "arbitrary" vertical system (Vertical is derived from the images or the GCPs and cannot be determined from ellipsoidal as an orthometric height. But Pix4D will do orthometric IF you are using WGS84 with an EGM gravity model and or you want to output in WGS84 with a EGM model).
I did several tests using Drone Deploy's Elevation Calibration tool so that you use ellipsoidal elevations for your images and control points, then obtain an orthometric elevation from a control points and adjust your elevation. I then compared it to an Agisoft output where the Geoid 18 undulation grid was used. In a 35 acre project area differences were in the very low centimeter range at the high end and were usually in the mm range. So this is a feasible option if you ever wanted to use ellipsoid elevations.
On another note, have you gotten any cool new jobs recently?