Hello Dan,
Since you are using itemType 1 and 2, the easier and fastest way to do this is thorugh a global table. (I have use FlexSim 2018 since your model is built in that version)
First, create a table like this:
You can use the name you prefer.
Then, you use the standar set size option in your trigger and put the dimensions like this:
This way, the size will be read from the correct table cell.
If you have any question on how to do this please let me know.