Raster Iteration and Raster Calculator Model

I have 2 raster datasets and I am trying to iterate through a "simple" raster calculation (Precipitation Grid + Residual Grid) for several hundred rasters.
I have created one Iterator model for the Residuals and used that as a sub model embedded in the main model which has an iterator for the Precipitation and the raster calculation. I've set parameters in my sub model so that I can call it in my main model and set the output name using inline variables to verify that the the model runs a one to one raster calculation but every way I've tried this it only adds the last raster in my sub-model to each iteration of the main model. I've tired a singular workspace using wild cards and variations of sub-model iterations all with no luck. I've also tried taking it back a step to a previous model where I created the precipitation grids and tried to embed an iterator sub-model there that adds the residual grid but also with no luck. I've attached my models but perhaps I am trying to go about this the wrong way...

HOW can I perform a one to one raster calculation for several hundred rasters?

Please, any help would be appreciated.
Thanks,
Melissa

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