About the fillet maxi impossible above to overpass in one shoot just Boolean Diff your object and make a variable Fillet on the other part! (on its own limits of course) ;)
Boolean union at the end if necessary...

So on the second part make a general fillet at the maxi of the first part
Then create your Variable fillet as you want with any variation admissible!

Here only one > 1
3 for example somewhere on the perimeter :)