I have tried the iFly737 in P3D4.2 at NZDN.
The first pic shows the 737 parked on the spot. Lateral alignment is good but is just a little high as you can see it connects about 250mm above the door sill. The curtain does not quite attach neatly but this could be in the iFly coding.
The next is the spawning position at Gate 1.
This is an AI 737 in the normal parked position on Gate 3.
I have very briefly experimented with moving the gates forward a bit in ADE. Seems to work ok with the iFly737 but the FTX one seems to have a few issues. This may be the door coding in the FTX model but I will have a look at this later. I did notice that Gate 3 seems to come in at a very slight angle to the gate position that is marked. I didn't have time to adjust that yet.