2 different models one for a 2D sprite for inventory and another for 3d in hand model for an item?

[bleedbluejrc]

could anyone give a very basic example of an instance in which IPerspectiveAwareMode1 allows an item to have 2 different models one for a 2D sprite for inventory and another for 3d in hand model for an item? I just don't understand how to do something like that, I've been looking up stuff an have no clue how to even start. 1.16.4

[ModMCdl]

Are there not parameters in the json modelling of the item to accommodate this? Most tools do something vaguely similar to this, and I feel like it should be simple to expand off of that.