[Fit Check] followed advice to size up and try 30GG and 30H, but can’t tell what size I actually am out of these two! (or if the straps will still be causing problems)

initial fit check for 30G linked HERE

ABTF Measurements:

Loose underbust ~30.5
Snug ub: 29.5
Tight ub: 28.5
Standing bust: 36.5
Leaning bust: 40.5
Laying bust: 38

Suggested size: 30FF/G UK

I bought a 30G of the Panache Envy and found that while it fit better than any bra I’ve owned prior, I wasn’t able to sidestep my major issue with it which was the discomfort / tightness/ random back pain that seemed related to the straps (I explain this better in the first post)

As per the advice of all the helpful commenters, I went up two cup sizes and tried them both with the Envy Plunge and the Cleo Blossom. After trying these on, I assumed the 30H Cleo Blossom would gap too much but here are pictures in the other 3:

Envy Plunge 30GG

Cleo Blossom 30GG

Envy Plunge 30H

There’s two parts of my question:

The first is that I’m having trouble deducing what size or shape I am from these photos, I don’t think my eye is trained enough yet.

I think the H cup definitely gaps at the top. I added a picture of me sitting to show relaxed posture - when my arms are at my sides (which they are most of the day) I can fit two fingers in the top part of the cup without manipulating the fabric. to an extent even the Blossom in GG gapped as well.

When I first tried on the H cup bra I immediately felt like it was probably a little too big in the cups. But after taking these photos, I’m starting to doubt that because I see it has a much more minimizing effect than the GG, in which my boobs still look pretty “boob-y”, and my understanding is a well-fitting bra should make you look pretty smooth from the front?

Am I just a GG with a lot of projection, am I wearing these wrong, or should I be going up to an H?

The second is most important to me since I went on this journey because of my back pain, and it concerns the straps.

I haven’t worn either bra for a full day yet so I can’t speak to whether or not these feel the same as a “too-tight” bra yet, but from the pictures alone I’m worried I’m hiking the straps up way too high on my shoulders / they don’t sit “naturally”. I feel like they’re bound to slip off throughout the day and I’m not sure I can blame the cup shape anymore. I’m wondering if it’s something about my anatomy (sloping shoulders maybe? Not even sure I have those) that makes straps such an uphill battle, and if I should be looking at any particular styles.

And if I do happen to suffer the same pain when wearing the bras for a longer period, what solution do I look for then? Are there other bras I could try/a problem issue I’m not seeing, or might it really just boil down to looking for the *least* painful bras until I can get a reduction?

Thank you so much in advance!! I really do appreciate everything this community has helped with.