FITTING: Reducing neckline gaping - hollow/shallow chest adjustment.

Diagnosing a hollow/shallow chest: On my bodice I noticed there was excess fabric on my front bodice between my 'apex' (nipple?!??!!) and the neckline. It looked like the top half of my bodice was "collapsing" on to my chest, because my chest was too shallow to hold up the bodice. Make sense?
This year I have become obsessed with achieving the perfect fit. I've spent way too many hours and dollars on making up dresses that don't fit well.
I'm no expert when it comes to pattern adjustments or fitting but these are techniques that have worked for me.
I basically make up the bodice muslin/toile, try it on, pinch and pin out the excess fabric.

The example above is my 'Anna' dress. I didn't do an SBA for my Anna (I did every other adjustment under the sun for it though, haha). The bodice fit well, but the neck line was wrinkly and gaping.
This is how it looked before I pinched out a 4cm wedge on each side of the bodice.

I transferred the 4cm wedge on to the pattern piece, like below (drawings not to scale). Once the 'wedge' is taken out, the neck line will need to be smoothed out.

The next example is my 'Georgia' dress. The small bust adjustment (SBA) solved the fitting issue in the 'cup' area of my bust, but the top half of my bust (nipple and above) didn't fit well into my bodice.

The (centre front) neck line was not sitting against my chest. I pinched out a 3cm wedge on each side of the (front centre) bodice. I transferred the 3cm wedge on to the pattern piece, like below (drawings are not to scale). Once the 'wedge' is taken out, the neck line will need to be smoothed out.
NOTE: Ignore the "SA 15"" on the drawing - I meant 15mm - not inches for the seam allowance!!

Call it neck darts, call it wedges, call it a shallow/hollow/caramello chest adjustment, whatever!!
At the end of the day, if there is excess fabric on the bodice, pinch it, pin it, then take that wedge out of the pattern piece.
I used to be caught up in 'defining' every adjustment that needed to be made, thinking that if it didn't have a 'name' or appear on Google search then the adjustment wasn't legit or correct, but ultimately, if there's excess fabric and if it's bugging you, get rid of it.
On both the Anna and Georgia, I have made a dart all the way to the seam allowance (SA) but every body will be different, so just transfer the adjustments to your pattern piece as per amount of fabric pinched out from your muslin/toile.
I hope this helps you if you are experiencing bodice fitting issues. My advice is always make a muslin/toile and keep persisting, the end result will be worth it :)