So as far as I can tell, the vitapod size is (local_depth + 1) * tier. If you open an energy door to get the pod, it seems to be an additional +1.
At the start, that's 1 at the party lobby, 2 at the first level, etc.
In the middle, that's 2 in the lobby, 4 on the first level, etc.
So what's the issue? This is out of balance.
For a party running from depth 1 to 7, you'll start with +1's, and end with +8's. You expect to have 4 people with values anywhere from +3 to +8 at the end.
And when you go deeper, you're at +2, +4.
So what can make this system better? Well, one method is just "depth", or "depth+1", rather than "local_depth". Then, you don't need to multiply by the tier group -- starting at Moorcroft (party lobby at depth 8), at depth 9, you'll get +10 pods instead of +4 pods.
Good? Bad?
If you think that depth 9, 10, should be meaner and nastier than 6, 7, then you expect the vitapods to be bigger at 9-10; the current system doesn't give you that. The current system makes you want to NOT leave the dungeons.
So, two questions:
1. Do you think the current system is broken, and needs to be improved?
2. Do you think this is a better solution? Do you have an even better one?
1. No.
The dungeons are clearly delineated by tier. Moorcroft to Emberlight is a higher tier than Haven to Moorcroft.
Each run between towns can be considered to be a complete game in itself, which differ in overall difficulty. The floor just before emberlight is therefore an "end game" floor of a medium run, while the floor just after emberlight is a "first level" floor of a hard run. There is no rule that says there must be a perfectly smooth transition between the last level of one run and the first level of the next, because they are not connected the same way two floors in the same run are.
In each run, you start out with small vitapods and then increase to larger vitapods by the end. The vitapods scale based on tier. This is balanced, just not in the way you are thinking.
Perhaps it would make more sense to think in percentages, rather than linearly.
In every run you start out with just a little over your normal maximum health. (Remember that in lower depths you will have better armour.) In every run you get to the end with about twice your normal maximum health. Thus in an Emberlight run, you get the same relative rate of health progression as you do in a Haven run. This is how it is balanced. I believe this to be fine.