I understand your frustration. No one said it was your problem. There are 1000s of things in Max that take some time to learn how to use and little documentation as to how to use them. If you took perspective geometry in school then you know how perspective and vanishing points work. If you break the two point perspective it just won't work. It's math and the 'Perspective Match' function is based on that math. So if you artifically modify and image and straighten anything, you break that math. Then Perspective Match wil fail as it can't figure it out. It's that simple.
The more you use a tool the more you learn about it and the more you keep an open mind to learning from others, then your knowledge will increase as well.
I'm terrible with Biped and I've spent hours trying to master it. It's not my fault or Max's fault that I have trouble with it and I can never seem to find the info I need to use it properly. Again, it's no one's fault. I just haven't worked with the right people or had the right people instruct me and get me going. Often doing tons of videos on Youtube will help me learn something I just can't seem to figure out. I'll often watch 3 or 4 tutorials just to finally see someone explain "that one" thing that was driving me crazy. It takes a lot of time, and maybe time you may not have when you have a deadline, but it is what it is.
Again, you did nothing wrong and no one is saying you did. There are just a lot of things in Max you have to figure out yourself and that's not Autodesk's fault. It's experience and it takes a long time to gain.
Rob Holmes

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3ds Max (2023-2026), V-Ray 7, Ryzen 9 9950X3D Processor, DDR5 128MB, Gigabyte Aorus X870E Master motherboard, Sabrent Rocket NVMe Gen5 M.2 drives, NVidia RTX 4090, Space Pilot Pro, Windows 11 Pro x64, Tri-Monitor, Cintiq 13HD, Windows 11 x64
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