steam Whac-A-Mole

Hi folks, I'm hoping for some help getting a handle on very inconsistent heating. I have a Burnham Independence boiler, installed about a year ago. The guy was not a true steam guy and reused an existing copper header (I know, I know), but it seems to still conform to the mfg minimum height-above-waterline requirements and not an inch more (again, I know that's not great to go off waterline). It utilizes a single 2" riser off the 2" tapping with an elbow to a 2" copper header section, which subsequently expands to a 3" black pipe header section just before it hits two 2" risers to the mains, then drops to a 1.5" equalizer. Water level is quite stable in the sight glass (though occasionally i see a drop of water drop from the top of the glass within the glass itself). I have a pressuretrol set to 1.5 with a 1 diff. Pressure generally seems to be somewhere between .5 - 1psi for the most part, though it's a 0-30 so imprecise. It doesn't seem to cut out except for when it's checking water level periodically. I have two roughly equal length mains at about 60 ft ea - one running primarily through the open basement and another that is largely running through a much shorter (in height) crawlspace that gets quite warm. The mains are not insulated (again, I know). The main that runs through the crawlspace has a Gorton #2 at the end and the one that runs through the open basement has a vent antler I built, consisting of a #2 along with two #1s. Pitches seem correct on the mains (more than 1" per 20ft). The crawlspace main has a mostly dry return, and the open basement main has a wet one.

Here's where things get strange - the crawlspace main heats about 2 mins faster than the open basement main, despite the extra venting on the open basement main. Not coincidentally, I assume, those radiators generally get hot quicker than the ones on the other main. Unimpeded, they get much quicker, even at the very end of the main. I have several of them throttled back to just over a #3 setting on adjustable Vent Rites, and then the rest with Gorton #5. The primary basement main uses Gorton #4s on its respective radiators (where thermostat is) with #5s the rest of the way. At the end of that run is a room with two equal sized radiators. the one furthest presently does not get warm. the one nearest gets hot as anything. Pitch on the far radiator seems fine, as does the pitch on the riser that runs to it from the main. That riser gets extremely hot quite early and then just hits a wall and stops to a near crawl. I remove that radiator vent entirely and occasionally a puff of air comes through.

The above is just how things are going now. It seems that when I make the slightest adjustments to vent rite settings on the hot side everything starts to change. That far radiator I mentioned actually was heating up fine a few days ago - pretty much in step with the other one in the room, but I suspect it was because I had been throttling the vent rite at the other end of the house to hardly anything. Once i touched that setting (opened it only enough to start venting) the radiator at the other end of the house stopped heating. Even now, I adjusted a couple of radiators on the "hot" side of the house simultaneously - one is still heating and the other has totally stopped, despite them also being in the same room and the same vent rite setting.

All of this to say - I do something barely noticeable in one place and suddenly something in an entirely different area goes lights off. Could all of this be due to the near boiler piping being done just to minimums? Could it be uninsulated piping? Neither seems the observable culprit (e.g. boiler doesn't seem to be surging and both mains seemingly fill ok). My boiler is slightly undersized (e.g. edr sits pretty much right between the two burnham sizes (IN6 and IN7) - but only after i had shut off one of the larger radiators I didn't seem to need based on heat loss for that room (turned the vent upside down to kill it).

I realize this post is as all over the place as my heating seems to be, but i just can't seem to get a handle on what's going on and it's driving me crazy.

Happy to provide any pictures or other details that might be helpful.