I'm no trainer, but spent a lot of years forging; can't stick weld to save my life, but can forge weld in my sleep. I have several thoughts.
* What steel are you using? The more "other" metals included, the less likely welding techniques used on common steels are to work; welds will often "stick"... but it's not truly welded.
* Are you sure you're getting your overlaps good and clean, prior to fluxing? Pretty hard to do, when the two pieces pre-riveted in place... which is almost necessary on pieces that small and hard to keep aligned from forge to anvil.
* Flux sounds good: borax, with a little sand, and maybe some iron. A little flux is good, but too much can complicate the whole process.
* Forge welding is the process of melding two near-molten pieces of iron or steel together: forceful hammer blows can ruin the whole deal, causing the two pieces to spring apart, just at the split-second they should be flowing together. Might try a little, uhhhh... push, with the hammer, and see if that makes a difference. Just use the hammer to simply press the two overlap into place; let the hammer sit for a couple seconds. Never know: that just may do it, right there.
* Another OIT an old commercial blacksmith taught me several decades ago: pre-heated anvil face, hammer head, and tongs are your friends. Anything your pieces to be welded will touch during the welding itself should be a little too warm to leave your hand against. It doesn't actually help you weld: but it prevents any unexpected drawing of critical heat from your work just when you need that heat in your work.
A slick way to preheat your anvil face is to use a good chunk of flat strap iron: heat that in your forge, and lay it on the face while you're prepping your work piece(s). Pull it off just prior to pulling your work from the forge. Setting your hammer head on that pre-heater while it's on your anvil, gets that done as well, without scorching your hammer handle.
* My last thought of the moment: make a few mockups, and try some different heats and techniques. More heat; less concussion; etc. You don't need to replicate the entire TG; just the same thickness, angles, and curves that you're gonna be welding on your finished piece.