I suspect your harshness is only indirectly caused by the gauge of the wire. I think it's more likely caused by the resistance you end up with. If you could wrap four more coils (without them shorting to each other), and bring the resistance up to the 2.0Ω range, you might find that the harshness is mostly gone, even though you're still using the same 28 gauge wire. You could also use thinner Kanthal, 30 or 32 gauge, and stick with the same number of wraps you currently have, again trying for something in the 2.0Ω range. What voltage are you feeding your 1.3Ω coil?
This is the part of making your own coils that gets to be fun... Experimenting with number of wraps, their spacing, and their thickness. Finding the supply voltage and coil resistance that works best with whatever kind of concentrate you happen to be vaping. You might find that wrapping a large number of coils with thick wire doesn't work as well as winding fewer coils with thinner wire (maybe because more wick is exposed?). Or you might find that a microcoil works better than either.
I'm very happy with the 2.2Ω Joyetech 510 Atomizers I was discussing earlier in this thread, for use with non-liquid concentrates. Yes they use silica, yes you have to rip out the bridge yourself, and yes, you don't get to experiment with different coils, but they seem to work perfectly, have never leaked on me (even when I grossly overfill them), and don't burn out.
(Sounds like my rant about the Sapphire clearos...).
I have hopes for the mPT3 to work well with Pure Gold (or a liquid concentrate I mix myself). I was not thinking about using them for non-liquid stuff though. I will not put up with significant leaking, even if it only happens 10% of the time. It looks like my mPT3's just made it through the local USPS sorting center, so I hope to have them tomorrow or Saturday. I plan on trying them with the stock coil first, as I want to see if they leak with the setup that the mfg provides. The type, thickness, and number of wicks often play a significant role in how well a clearo wicks and how much it leaks. Before I wrap a silicon wick with my own wire, I want to see if the mPT3 wicks OK and DOES NOT LEAK on it's own. If it performs well, then I'll try what you're already trying. That way if it starts leaking with my coil setup, I can look to add a "flavor" wick, and see if that "fixes" things, etc. I also plan on starting out with plain VG, so I don't waste a shitload of Pure Gold only to discover I screwed something up.
I also want to try the mini aerotank when it comes out, though again I'm looking for a Pure Gold solution, not a non-liquid solution.
Onward Thru the Fog