E# or F Natural
Adding the accidental E# (my) to F# natural minor creates a leading tone and changes the mode to harmonic minor. Notice that E# looks and sounds exactly the same as F natural; they are, in fact, enharmonic with one another. The choice of E# over F natural has everything to do with maintaining scalar appearance. For example, consider the following example:
In addition, E# to F# looks like it functions as a leading-tone; F natural to F# does not. In order to include A on ① in the F# harmonic minor scale, the left hand needs to temporarily shift in and out of Pos II. This will be a glide shift, involving “1” on ① when moving from E# to F#.