Dynamic transition lengths?

Hey, I’m a media composer, not really an expert with Fmod so far.
I need to make transitions between different pieces of music as it is pretty standard for gamemusic. I have a parameter set up that let’s me switch between those pieces at their relative points within the timeline which is good.
The problem are the transitions. I can set up desination regions/markers to make transitions between the music pieces but only with a predetermined transition-duration. I’d like to have a parameter that controlls the duration/speed of the transition. Tried a couple of things, had some serious arguments with ChatGPT, nothing worked so far.
Any clue on how to achieve this?

Try this out: Make two transition regions, and set their destination to the same place, but one of them make a short transition and the other, make a long one. Make a transition speed parameter, and coordinate conditions with that param in the Transition Conditions. These screencaps below I didn’t complete — didn’t add the fade-in on the second region, but you get the point. Let me know if you need more info and I’d be happy to clarify!

Long Transition:

Short Transition: