What you need to do, and I don't think it is in the Vid, is , at the end of the FG - when you do the half hitch to finish, PULL THE WHOLE THING TIGHT. As tight as you can. This sets the knot. Like TK, I pull the thing tight, each wrap, as you go. Keep tension on. The rest is cosmetics. The knot is done. But pull the thing hard before cutting the last of the mono off. I melt the last bit of mono , but I suspect not needed. Then also not in the vid, I finish with a bunch of reversing half hitches L-R-L-R, after the mono, then double back same. Then finish with a double half hitch and I use a drop of supa glue on that tag end. I know many don't like it. It just stops the tag end coming free after multiple times pulled thru guides. And the two layers of half hitches smooths the transition between thin braid and thicker mono. If I was still at my rods as this morning I could take several pics of them all rigged with FG knots - braid on reel, mono leader. Some been there a yr or more, and used weekly if not more.
Alan