Tiles cannot be changed to other sizes.
And the larger sprite will be centered on the regular 32-grid, so part of it will overlap into the next tiles (like the wall). To prevent that, you have to make sure that the space next to the wall is also impassible, preventing the character from moving near the wall (that can be accomplished by making an impassible floor tile, by using a script like Yanfly's restrict region or by changing the defualt movemen/collision area with scripts).
If the sprite stops 48 pixels from the wall when going down, then you have added scripts for collisions OR made wrong passabilities on tile regularly, while the sprite can be any size, all movement and all collision detection is still based on the 32x32 bottom center of the sprite.
Follow the link in my signature to the sprite explanations again, either you made the sprite wrongly or you missed the ! in the filename.
By default, Ace assumes that the feet of the sprite touch the bottom end of the picture - if you have any transparency between the feet and the end of the spriteframe, that will displace the sprite from the grid.
However, on any tile set as grass/bush in the tileset settings, the bottom part of the sprite gets turned invisible to give the impression of walkin in grass - the ! in the filename ist the keay to disable that (usually for doors or similiar objects.