It’s 1 - friendly onatel, since there’s only one tile’s worth of energy to divvy up. So:
Enemy gain = (1-p)/(1-pq)
The calculation assumes a whole tile of mana gain at the start, so the mana rounding factor is baked in. If you want to convert to % of a bar, you need to divide by 10 since they’re both average mana (or 9 if someone has high level mana troops).
Here it is as a table, in tiles:
| My Onatel | Enemy Onatel | My Gain | Enemy Gain |
|---|---|---|---|
| 0.25 | 0.25 | 0.200 | 0.800 |
| 0.5 | 0.25 | 0.429 | 0.571 |
| 0.75 | 0.25 | 0.692 | 0.308 |
| 1 | 0.25 | 1.000 | 0.000 |
| 0.25 | 0.5 | 0.143 | 0.857 |
| 0.5 | 0.5 | 0.333 | 0.667 |
| 0.75 | 0.5 | 0.600 | 0.400 |
| 1 | 0.5 | 1.000 | 0.000 |
| 0.25 | 0.75 | 0.077 | 0.923 |
| 0.5 | 0.75 | 0.200 | 0.800 |
| 0.75 | 0.75 | 0.429 | 0.571 |
| 1 | 0.75 | 1.000 | 0.000 |
| 0.25 | 1 | 0.000 | 1.000 |
| 0.5 | 1 | 0.000 | 1.000 |
| 0.75 | 1 | 0.000 | 1.000 |
| 1 | 1 | Diverges | Diverges |