Let's talk about ignite and ailment threshold

I think I have the basic info down:

Ignite magnitude and chance is now solely dependent on the raw hit (fire) damage. Both are calculated from the hit damage before mitigation, so mob resistance in particular is irrelevant for this purpose.

Ignite magnitude is 20% of the igniting hit damage, per second (and lasts for 4 seconds by default). It can be explicitly scaled by some nodes on the tree. The burning damage on the mob is then subject to resistances - it can't penetrate, but lowering resistance will help.

Ignite chance is 1% per 4% hit damage relative to ailment threshold. In other words, if the hit has an amount of damage equal to 100% of the mob's ailment threshold the chance to ignite for that hit is 25%.

From what I understand, ignite is now basically more like an alternative vector to scale hit-based builds other than going crit. Though confusingly, in principle it seems very viable going both crit and ignite, since critical hits will have a higher chance to ignite and apply stronger ignites by virtue of hitting harder. In practice, scaling both crit and ignite might not be feasible, of course.

Here is my main question: Do we have any idea what the ailment threshold on mobs is? Is it some percentage of max HP, is it a fixed amount per mob rarity, possibly scaled by area level?

Whatever they are, are ailment thresholds simply too high? From what I can tell, we have to chunk mobs so hard to get a reliable chance to ignite them, that the ignite itself becomes basically irrelevant.

Due to some unfortunate real life incidents I'm only in Act 3 yet. I like the (admittedly very basic) idea of going fire skills on an Infernalist and want to explore ignite. I was obviously counting on Fireball to be viable. However, outside of the guaranteed effects from Flame Wall and Solar Orb, ignites are simply not happening, even though my Fireballs are doing decent damage in principle. I even have the +100% chance to ignite support on the skill and roughly an additional +80% on the tree. I'm not expecting an ignite on every hit, but shouldn't it be semi-reliable by now? Most mobs in my non-rigorous testing die from pure fireball hits without ever igniting.

Very confusingly, I'm using Spark + Flame Wall as my main source of damage until I figure the ignite stuff out. And the Sparks are actually shocking enemies occasionally, even though I have absolutely no other support for chance to shock. Is ailment threshold for shocks different? Maybe it's simply a numbers game since there are many more Sparks flying around than Fireballs.

Pretty basic bonus question:

• Does increased fire damage scale ignites themselves (not only the igniting hit)? Or is magnitude the only relevant modifier?