Tested your procedure, It works fine for me, also.
And yes, after a test shot with only few seconds of exposure, ETTR is able to correctly expose the second shot ( aprox. ~ 1 minute exposure ) So no need to waste time in a very long test exposure, that's great !
I do not see any need to change the highlight ignore setting, I get the exposure that I like ... but I always set lower ETTR's SNR limits (4 EV for midtones, 1 EV for shadows) than default ones (6 EV for midtones, 2 EV for shadows). The reason is that I capture mostly landscapes, and I don't want that sky highlights get clipped at all. If the foreground gets too dark, I use Dual-ISO or bracketing.
If you feel that in long exposures you are getting underexposed images, you can increase the highlight ignore value, as you have done, or alternatively increase the SNR limits. I think the second method is more reliable to expose more the shadows and midtones, regardless of the presence or absence of specular highlights.