I have never had this issue and I am an avid photographer. I slow down and look a lot.
It is physics, if you don't want the opinion....the vertical height of the 120 is such that it causes the tank to want to find a lower point...much like balancing a pencil on your palm, vertically--you have to continually adjust the palm so that the pencil stays straight up and down....
When you come to a near stop, or to exagerate the effect, a dead stop, there is no airplane wing action of the body left to stabilize the tank....the tank is higher than the bc or wing, so it wants to fall to one side or the other...
The other side of the spectrum is double 80 cu ft tanks with a 40 pound wing....the tanks are low to your back, and with a much lower center of gravity than the 120....and the wing extends out around the outside of each tank, to the top of it, so with a couple of pounds of lift( gas) in the wing, it acts like pontoons to create an amazingly stable platform.
Using doubles creates another set of issues, mostly the need to create an easy system for how youy move them for filling, how to move them from car to boat, to garage, etc...not a big deal, but much better if you actually find an optimal way for each, and don't handle the same way you would with a single 80.
For 2 tank boat dives, a trans-fil whip and a hp100 can put enough into the doubles for the 2nd dive, to make it better than the 120 for a 2nd dive....no trans fill after first dive, and you have to plan each dive more like it is with a single 80, or you will end up with shorter 2nd dive than you want.
I used to use lp 120 tanks for underwater video of the reefs off Palm Beach. When cruising, they were awesome tanks...streamlined, and easy to deal with.....On shipwreck penetrations, where it gets tricky and tight, and you are moving slow, I would not really be thinking about the 120 and how I had to be on "auto trim adjust" throughout....I did not notice this, until I went through a GUE Fundies class, and had to spend hour after hour nearly dead still...and as you are forced to concentrate for this long a period in 6 foot deep water, it exaggerates the annoyance factor for the lack of stability in the 120 cu ft tanks. When you switch to double 80's, it is like being able to take a nap, stability wise.
For a macro photographer, during the hovering and slow movement, this will be a real improvement with the double 80s....However, if there is any surge or any current, when you finally find your shot, you will most likely need to get heavy, and "become the bottom"....certainly with nudibranchs and other very small life when muck diving with the lens choices this will involve. So the hover is better for double 80s, the "becoming the bottom" part will be fairly similar if you get very heavy.
If you were shooting macro over delicate coral reef, then the double 80's would blow away the 120, because there is no place to get heavy on, that would not be catastrophic to the coral.
