My initial testing with R5 (with arraywrite, but R5 is still pointer for that) is that it points to array ram location plus array position
so to find position in array, you have to subtract the base value from R5. You can find that in LIST file or declare location for array:

array1 var byte [100] $100 'start array1 at location $100, 256 dec in ram

so you know base val to subtract ??

don