I haven't seen anyone mention it, but there are some really bizarre inconsistencies with Immersion and Arcane Torrent in particular with regards to level scaling. I've been looking to update the spreadsheet to include fields for skill levels for Immersion, Arcane Torrent, and Mana Sweep to track Tooltip changes based on skill levels and mana changes (an extension of the current goal of making gearing decisions less of a crapshoot), and started noticing very early on that the Magic Damage/ Max Mana component to Arcane Torrent was showing different results almost every time I would look at the skill tree.
The skill gains .5 min and .5 max damage to both current and total mana scaling per allocated point, at alternating intervals, so (because of D2 always rounding down) the min and max will increment by one whole percentage scalar every other level at alternating intervals. But the Total Mana numbers weren't always obeying this rule, instead sometimes jumping an extra increment. At first I thought it was rounding down at even levels and up at odd levels, but now on further inspection, it seems to be gaining damage scaling based on character level as some sort of hidden synergy, at least up to a maximum percentage (possibly simply up to a maximum combined value between skill levels and character levels).
In addition, Immersion has shown some inconsistencies, where it starts with 20% of missing mana as damage, and gains 20% for every other point starting with the second, so 20, 40, 40, 60, 60, etc. But on at least one occasion, I observed the "Next Level" value change, where with 4 allocated points, the next level was showing 60%, as it should, and then a few minutes later started showing 80%, still with 4 allocated points and no bonus to skills.
Even more bizarre, after doing a full skill/stat reset through Akara, the first point in Immersion is now worth 40% instead of 20%... There's clearly a hidden scaling factor here, and I can't seem to figure out what it is, although I'm absolutely convinced it's relative to character level and not Energy, as a fresh stat/skill wipe is producing these inconsistencies without allocating stats. Furthermore, these numbers don't track with what's showing up on a Lvl1 Character, nor on a 136 main with no gear or charms, and it's also observable on Mana Sweep, now that I know what I'm looking for. I'm uncertain at this time if this is consistent across other skills and classes, or if it's specific to Arcane, but I'll need some time to reverse-engineer the curve if I'm going to follow up on having a tracker for the spreadsheet.
For now, though, it's something interesting to note that even at the skill cap (and when potentially plateaued on charms), there's still room to grow damage numbers simply by grinding out another level or two.