Did some testing because I wasn't seeing range increases out of my miners. The following is with only the Space Age "mods", Blueprint Sandboxes, More Quality Scaling, and Mythic Quality (Normal Scaling) installed:

Is it intended functionality that Common and Uncommon, Rare and Epic Electric Mining Drills share 5x5 and 7x7 area expansion with Legendary at 9x9? Note: Speed increases show up as expected.

Burner Mining Drills from Common to Epic are stuck at 2x2, and then Legendary jumps to 4x4. I assume this is not intended, because for the Mythic-Singularity qualities you get:

Mythic: 13x13 range Electric, 6x6 burner area
Celestial: 17x17 range Electric 8x8 range burner
Singularity: 21x21 range Electric, 10x10 range burner

I assume that this is something to do with a formula somewhere, because as soon as you jump out of Vanilla qualities you suddenly see the ranges going up as intended. If this isn't intended for burners okay I guess but I was personally expecting 3x3 range from the Burner at Uncommon and increasing by a tile each level, and 5x5 common length from electric smoothly going 6x6, 7x7, 8x8, 9x9, and 10x0 at the final like we see in the Big Mining Drills going up 2x2 tiles per quality level (13x13 becomes 15x15, etc, with a 4x4 jump from epic to legendary)

This is working as intended, but I admit that I'm not confident that this is the best possible scaling.

The issue is that normal mining drills have a 3x3 footprint, and burner ones 2x2. Giving a normal mining drill a 6x6 mining area means it would be off center from its own footprint, and there is no obvious direction in which the mining area should be extended. A burner drill with a 3x3 mining area would similarly be asymmetric.

For drills with larger mining areas, this is no longer a problem, since you can give each quality increment a +2 area boost.

If you have another idea on how mining area should ideally scale, I'm definitely open for suggestions.

TLDR Suggestion is to set non-Big Mining Drill range increases to odd-numbered Qualities, including Burners

Yeah, uh, the footprint thing I forgot about, derp, I'll admit.

I was playing, until recently, with the Lignumis burner mining drills which by default have a 4x4 mining area, which is super nice, and now I'm back to the regular ones that don't extend past the actual drill's footprint. Which threw me off a bit because I forgot about that

To make the Mining Drill jump in quality worth it, I have a suggestion:

Common/Default, and Uncommon Burner Drill: 2x2

Rare and Epic (level 3, "maximum" upon unlocking Quality) Burner Drill: 4x4

Legendary Burner Drill: 6x6

This would put the area gains on par with the Electric drill (5x5/7x7/9x9 at odd-numbered Qualities) and would only reach base Electric Drill coverage when the Electric Drill would be at 9x9 (and realistically be looking at 19x19/23x23 big mining drills at that point).

How would you deal with drills with other base areas? The area scaling should be sensible for any base area, from 1x1 to 100x100 or even above.

Eg. there is the "Ancient Drill" mod that adds a big mining drill with a base area of 25x25, but there are also some mods that add intermediate tiers of mining drills between electric and big.

Would 1x1 drills also get range buffs at rare and legendary (3x3/5x5)?
At what base area would it change to a buff at every level, or to 2 per level?

Currently, the scaling is:

(for burner/electric/big mining drill, ancient drill and cubeine giga thermal drill respectively)

This follows from the following formula: radius = base_radius + math.floor((base_radius+1)*quality_level*0.15) (ie. add 15% of base radius + 0.15 per quality level, then round down).
What formula would you use for arbitrary base areas?

When designing the formula, I tried to get a scaling of 5/5/7/7/9 for the normal mining drill and 13/15/17/19/23 for the big drill (since this is the drill that's probably used the most and the most intuitive scaling works well there, these numbers should stay consistent in any alternative formula; the numbers for the electric drill aren't as important to me, but 5/7/9/11/15 would have been pretty absurd).

The admittedly uninspiring scaling for burner drills naturally followed from linear formulas under the above constraints, and since you typically only use them briefly at the start of the game, that didn't seem to be a big issue for me.

I did some more calculations, and it would be possible to achieve a 2/2/2/4/6 burner drill scaling with a linear formula (the upper right corner of this graph: https://imgur.com/a/jwMyZRu at (0.11,3)), but these values seem significantly less natural than the (0.15,1). Replacing the floor with a round or ceil would make matters worse for the burner drill (it would get negative buffs if a linear ceil formula was fitted to the desired values for electric/big drill).

For any other scaling, you'd need some more complicated formula for the per-quality offset as a function of base range...

I........don't know have any idea about the math. the burner miners just felt off to me

Fair enough. Maybe I'll add an option(/change it?) to specifically buff the scaling for drills with less than the 5x5 area of the electric drill...