Both my sons have been diagnosed with reflux, my youngest not as bad as my eldest, thank goodness.
My pead recommended for both my boys to give the antacids and never mentioned about changing formula (though I was still BF). When my eldest did start having formula I didnt put him on reflux formula, I used 1 that agreed with him and continued with the antacids and that worked for him.

I was happy to use the antacids only because I knew what it felt like when I was pg and had heartburn both times and I didnt (and still dont) want my sons to hurt like that. But thats just my opinion.
The formula just thickens the milk and puts a lining on the babys stomach so they dont vomit as much, I dont think it actually stops the burning from the stomach acids, but Im not sure.
1 thing I would recommend if you havent already done so is to elevate Annikas bed so shes not lying flat, this helped my boys. Oh and if you're not against them, dummies do help keep the acids at bay. The sucking is a relief, though my youngest doesnt like it.

I hope this helps.