adding arpeggios to a chord crowds the altered notes - solution
I found that in many cases (but not always), when adding an arpeggio to a chord containing one or more altered notes, the arpeggio symbol will crowd on top of the alterations symbol(s) if I select a non-altered note (pic : arp1.) of the chord to position the arpeggio symbol .
However when I select an altered note, the crowding NEVER occurs (pic : arp 2.).