Jan 12, 2021
Well, I dunno. On an A harp tuned to 443 I can bend the B in hole 4 down to an A, albeit 30 cents sharp. I have the tip of my tongue touching the harp and am basically "humping" the tongue back into the cavity of my soft palette. Some people describe this as opening their throat and claim to be bending from the throat. It can feel like that, if that's where you focus your attention, but it's actually a combination of factors, or a coordination of movements involving much of the vocal tract, which is dominated by the tongue and glottis and driven by the diaphragm.
As to the 3, which is a natural G# on the A harp; it will bend to a rather sharp E in my mouth. About 40 cents sharp of the E in blow 3.
I remember when I obtained my first Low F, I could not bend the 1 draw, and found the 2 draw rather a challenge.
When I a asked for advice on MBH, the first such was "umm, practice?".
I didn't find that very helpful at the time, although it's essentially correct. There are ways of practicing though.
I think the advice above, about using a higher key harp, will probably help, although I'm sure you'd get there on the A as well.
You need the right embouchure, and the embouchure needs to develop strength and coordination. You can't really force those things, but you can encourage them. Playing on a C harp may well help, a little like weightlifting. When you start out you simply don't have the strength to move the big weight and you can spend a long time trying and getting nowhere and not be a lot better off. If you start with something you can actually move, you will develop more quickly.
And keep at it. You know the type of movement that's needed so keep on trying and you will get momentary successes. Gradually you will learn how to make those more frequent and as you do you will develop your coordination and control over the muscles you are using to get the sound. It really is a lot like learning to speak. There's a lot of experimentation going on.