Scale Run Structures
When writing runs for any instrument that is capable of playing runs, you should stick to plausible scales. Instrumentalists practice their whole life to play scale runs in any form – upwards, downwards, starting on different scale degrees etc. However, if you write something that is not a “common structure”, like a chromatic run but somewhere in between is a whole tone step, it will be definitely something that will cause problems.
These structures can’t be easily recalled from the muscle memory like all the other scales. So your players will most likely trip over these “odd” tones, especially when they need to play it more or less sight reading. The bottom line is to avoid being overly fancy or just not thoughtful on scale runs.