Draw two keyhole

Good morning crossover. Let me restate your question to make sure that I'm following you...

Using a Bb Harmonica, playing the 2 draw creates the note F. When playing a 2 draw whole step bend (2") the note Eb sounds.

You say you're using "taaa" to sound the 2" and "iiii" to sound the 2.

In English, the "a," when associated with "ah," like the last part of the word "spah," creates an open mouth cavity in the back, with the jaw dropped and tongue lowered. This will create a nice embouchure for an unbent note. So, "ah" is commonly associated with an unbent note.

When performing a bend, "oo," like when saying "too" without the "t," is associated with a bend. When creating the 2" I commonly recommend students use "koo" or "too" with or without the "k" (tongue blockers) or "t" (pucker players) articulations.

So... "ah" for non-bend and "oo" for bend... or tongue lowered (especially the middle and back) for a non-bend and raised for a bend.

Hello from Oahu, HI (family vacation right now). 3 draw bends are very challenging... focus on using more of the front of your tongue further forward in your mouth for the 3', more of the middle of the tongue for 3" and more of the back of the tongue for the 3''' (though it's not a good idea to practice 3''' right now... it's not commonly used in 2nd Position playing and can cause problems at this stage of your training).

You can try "she" for 3', "ee" for 3" and "ooh" for 3'''. Again, you'll need to experiment, these are just general locations.