Samsung 25R's are solid down to .25....I use them on my tube mechs with my .24 single parallel 24 gauge builds that are 3.2 mm inner diameter and 5 wrap and they work just fine....anyone who's read my rants knows that below .2 on a single battery tube mech in my opinion is pushing into dangerous territory I can't recommend and use at your own risk.
I agree that simple parallel builds are great for improving both flavor and clouds. My favorite is the single coil version I mentioned above or a 26 gauge Kanthal dual parallel coil build with each of them 7 wraps around a 3.2 mm drill bit also metering around .24 ohms. Again, I use that with my Samsung 20 and 25R's and my LG HE4 with no problems. Even if it could use the full 4.2 volts it still tops out at 17.5 amps and my copper Nemesis seems to be the lowest voltage drop of my single battery mechs and with those batteries fully charged I've never metered it's output above 3.7-.3.8.
If you must go below into the red zone below .2 ohms then a VTC 3 is my best recommendation. yes it has less mah than a VTC 4 but it's actually a better preforming battery and with a build that low you're only going to loose a couple draws at best before you'd have to switch anyways. Next recommendation would be a VTC 4, then the new LG HB6 if you can find it (also a 30 amp continuous drain battery,) and lastly a LG HD2 25 amp continuous drain battery. those will give you a little more room for error or something to go wrong, and safer performance.
If you choose to go that low with one battery I wish you the best of luck...but I cannot endorse or recommend it...especially with so many great regulated high wattage mods on the market today and more an more dual to quad mech boxes coming out in both series and parallel versions. Vape safe...try a higher resistance parallel or twisted build before going any lower please....please?