You didn't say what kind of mirrors you are fitting. Operating on the assumption that it is the "bullet" type mirrors that were supplied under the accessory "HAC" part number series and shown in his avatar, TR4nut has pegged about as good of a position as possible for the mirrors. This is especially applicable to the one on the right hand (passenger's) side. Any more forward than that winds up putting the windscreen frame in the way and any more rearward starts limiting the utility of that mirror. You can play around with the positioning by using some really good, but releasable tape to hold the mirror in place and then seeing how that placement works from your driving position. Start with the passenger's side and once a position is determined, go to the drivers side at the same relative position and confirm that it works for you from a symmetry standpoint. If not try small, incremental movements until you are happy with both the placement and view from the mirror.