In an effort to boost my pressing ability, I have been practising bottoms up presses and I'm really happy with how tight and locked in I can get. The issue I have is when I move back to pressing with a heavier bell, I find I can't maintain that same level of tension.
Does anyone have any tips aside from, obviously, spend more time practising?
This is interesting. Adding instability to a movement does not increase your force production - quite the contrary. You can never squat more on a bosu ball than on flat ground, always less. Also why you can leg press more than you can squat. The more stable the movement, the more force you can produce.
You, however, talked about
tension, and that can definitely go
up with increased instability - precisely because of your need to stabilize your body. It's why we produce more (full-body) tension when squatting then when leg-pressing, to keep using the same example.
So you see how, apparently, no, there's no way to
reduce instability and
maintain requirement of tension; you can keep practicing, as you said... but this all has given me an idea you might find useful.
In addition to pressing the heavier weight, do sessions of one-handed swings with it. If it's heavy enought to disrupt your posture and it forces you to really lock your abs, your shoulder and your a#@ in order to avoid rotation, it might help you work tension as a skill with that weight until you learn to press it bottoms-up.