tl;dr -It's just an artifact of how the datamine was originally coded. Values shown at 10% for REC bonuses in HoT/Burst Heal enhancements are actually 0 unless the enhancement is adding it as a new effect.

This testing was done using my recently maxed Holia, to be sure before I post a full analysis on Neferet in a couple days time.

I used a unit with 2530 REC post-buffs in my squad (a Anima Tubro Cyclaw, for anybody wondering - the REC was checked using in-simulator stats after buffing) and tested healing values with Holia's enhanced HoT effect. This test was repeated until multiple values outside of one of the possible ranges had been confirmed.

Expected values were found as by adding the potential REC values (15% = 380, 25% = 633) to the minimum and maximum possible HoT ticks (4000 - 4500)

Because the range of healing I got showed values impossible for the 25% REC version of the HoT range, I've concluded that the 10% REC extra shown in the datamine isn't real.

So the next reason is to consider why. I've been working with the datamine for a long time, and in many cases it's coded to show default values equivalent to what the game sees to make things more understandable for users.

In the case of healing, variable REC bonuses which are coded as 0 are treated by the game as 10% (other values are actually interpretted by a formula into their final value, but when you plug in 0 you get 10%). Because this is always the case, to make it easier on readers Deathmax simply shows the final REC bonus after the game's formulas would be applied. Another issue which would make it not reader-friendly if we went with just showing the variables is that for whatever reason, REC multipliers in healing effects actually have two separate variables.

In the case of the REC bonuses shown in SP enhancements, however the datamine has no way of knowing what the values of the enhancement are relative to the skill being enhanced, so it interprets all "enhance skills" as "add skills". This has resulted in "enhance burst heal" and "enhance HoT heal" SP enhancements showing incorrect REC bonuses which has convinced people (including at one point myself) that they increase the REC modifier, but they actually don't.

So for healing effects, it's likely enhancements only increase REC value if a value other than 10% is shown, or the enhancement is adding the heal as a completely new effect to the skill.

For what it's worth, I took some time to check out how the REC bonuses from stacking multiple HoTs stack, and multiple HoT effects definitely trigger separately and use their own REC multipliers, e.g. Holia SBB HoT Beiorg's Armor = 15% 10% = 25% REC modifiers. This much doesn't go against what I've said in the past.

There aren't many other cases in the datamine where a default value is shown for variables which = 0, so this issue is unlikely to occur elsewhere. There are cases like hit count buffs' damage modifier where the value shown is relative to 100% rather than relative to 0% which has led to confusion with things like Savia's UBB, however. As I expect these I typically give the correct values in my analyses.