I can't imagine the somewhat tiny increase of PG from the nic base would cause such a harsh throat hit to say, a 30ml mix (if that's the amount you're making?). It could be the "quality of the nicotine" in the PG base? Now, I've never used ECX nic base, so I couldn't tell you what to expect; you'll have to do some research on what others have experienced with ECX nicotine.
Buying a titration kit and actually using it to test your nicotine is always a good idea. One should start there... then move on to other issues. Purchasing or requesting nicotine samples from other vendors is a good thing to do as well...
There's plenty of Nicotine talk right here on ELR:
But, there are other sources as well:
Quality nicotine can solve a lot of issues, with regards to throat hit.