I like a lot of flux. More then many feel is needed. I find it's easier to soak off flux then to sand down oxidized/torched surfaces. I will sometimes use flux placement as a way to control where the filler goes but with brass that's not a sure bet. There have been MANY frames built with brass but without flux... Heat control, gravity and filler rod initial placement are the main ways i limit the filler's movement.

An example of this is with the recent practice joints i posted. After a flowing into the tubes' contact surfaces to establish an internal presence of filler (nut always a full fillet but insurance that you got full penetration) I adjusted the flame to be a bit smaller (still neutral) and brought the flame closer to the joint's crotch. By flicking the flame away from the crotch i can control the temp there and not let the tubing away from that spot get too hot. Place the filler rod into the crotch/flame, melt off a blob that wets out to the tubes but does not flow because the temp is not that high, move the flame along the crotch and repeat. After a 1/2" or so of raw fillet has been deposited I will go back and, with the flame running over the raw fillet, sculpt the fillet using the flame's cone to focus the heat just so. dabbing or flicking with the flame gets the raw fillet up to the temp it starts to move (but not flow) and having the place where you want the fillet to expand to hot already will make the filler more there. Too much movement and you flick away the flame, reposition the joint for gravity to aid the filler's movement back and repeat to reestablish the fillet's shape. I am not yet real good at this but starting to get a good feel of the flame placement and temp control.

The big problem I see some doing (including me when I'm not focused) is to get the joint too hot when laying down the fillet of shaping it. It's easy to have the flame heat up an area past where you're looking and disturb the fillet's shape there, not knowing this till you think you're done. You defiantly can't add filler to a fillet with too little heat, the filler will ball up and roll off (watch those feet of yours!). But you can delude yourself in thinking you can make a fillet with too much heat, the filler will willingly be added, just end up gong where you don't want it to be because it flowed to the hot area. So the trick to control where the filler goes it to control where the hot area is, and isn't. Andy.