SR20DET trigger offset

Hi everyone , I’m wanting to discuss trigger offset for the SR20DET to see if I can get a better understanding of how these trigger types work … on the factory trigger wheel I’m seeing about 109 degrees to sync timing on multiple SR’s using haltec esp software .. notch top and non VCT engine both seem to sync the same degree … I understand that the trigger wheel has 360 markings around the exterior and 4 dissimilar windows for the home signal .. sense most 4 cyl engines fire 2 up 2 down I’m wondering why the firing angle would be so far from the math it suggest it would fire at (or maybe I’m missing something ) as a full rotation of the engine cycle is 720 degree wouldn’t each cylinder 1,3,4,2 start to approach TDC let’s say 15 degree btdc every 180degree ? 180-15 =165 why are we syncing at 109 ? Maybe falling edge of the last window being that they are not equal length ? The reason I ask is because I’m using a different platform that cannot fire sequential ignition this time so I’m running waisted spark on 1&4 and 2&3 using a 12-1 trigger disk and having firing problems .. I came across a bit of info that suggest if your trigger offset were 180 out that the engine could still fire and run if using waisted spark but the injection timing would be wrong .. I have a feeling this may be the cause of the problems I’ve been experiencing on this budget ecu I’ve been dealing with .. can anyone help me understand the maths here and possibly elaborate on the 12-1 trigger ? Thanks in advance for reading !