What you're experiencing is exactly the limitation I came up against about a month ago. I wanted a sketch object to control the horizontal placement of some text boxes. I had originally wanted to create an auto update function that would use the length of the input property or parameter to update this value distance on the fly. However, You cannot gain access to either parameters, or properties within the sketch itself. Not allowing you to simply update the value behind the property. You can further confirm this by attempting to drop down the "list parameters" when within this sketch to see that no options populate.
I was able to recreate the user inputs and order of operations to create a function that edits these sketches dynamically. However its no longer an automatic. A rerun is required due to the recalculation that has to then be passed into this dimensional constraint. A real downer in how simple an automatic I could have made it function.
You're not crazy, and something like sketched symbols operate similarly in that they cannot access parameters only properties. Meaning I have a ton of parameters as inputs that then get passed to the properties using an automatic function to keep them together. To be clear I have multiple parameters that make up a single property, that then gets displayed within a sketched symbol. To keep the values of the parameters in line with properties, I have an automatic function that runs reassigning them as needed.
