I found a setup on how to position Mario for 1-2G. It's a consistent way to position Mario because it sets up Mario to jump near that perfect location instead of Mario running on the elevator. You can do the setup in 2 different ways but are basically the same. This is how I do my setup.

This is how how RoyLGamer does the setup.

This clip shows how consistent the setup is for positioning Mario. The top left of the game screen shows Mario's sub-pixel position, and for most of the times Roy has done the setup, he gets 2D0, which is the perfect position for Mario to do 1-2G. https://www.twitch.tv/roylgamer/clip/ArborealBlatantSandstormPunchTrees

I call the setup ytman setup, because I'm not creative with names.

Additional info: If you jump one frame early from the long platform, Mario's sub-pixels would end with CD0, and you would have to run one more frame from the elevator and jump to get the perfect position. If you jump perfectly, you would end up with F50 and you would have to jump immediately from the elevator.

CD0 image: https://imgur.com/a/Pym7CEM F50 image: https://imgur.com/a/IUiPTrC

Shoutouts to DKR_02 for finding out this additional info and RoyLGamer for testing out my setup.