Drum Roll (tremolo) marks won't go where needed on a whole note

I'm attempting to mark a whole note with tremolo (duple slash) markings to indicate 4 beats of roll. Clicking on the whole note in the 'C' space of the staff (allocated to the Snare Drum on a Percussion staff) and then double clicking on the slashes under the tremolo menu, it puts the slashes UNDER the note which is a problem since on the percussion staff, elements played with the hand have the stem above the note and those played with the feet have the stem below the note.

The fact that it puts it there is not the problem and even makes sense, as on any pitched staff it usually would be correct placement for a 'C' note. The problem is that once it is there, it cannot be flipped with 'X' and cannot be manually moved. As an aside, a half note puts the slashes where I want them (probably guided by the stem) AND can be flipped with 'X'.