thanks to both of you for the answers. yes..thats the logic i guess. otherwise he would write also in front of the left hand staff 8va or he would write it just in the middle for both of the staffs...even though left hand has the same key signature..i would get surprised if it would affect both..
about the octava bassa...you are right.but sometimes it is written 8va bassa not 8vb.. for example in one piece of robert delanoff i see it right infront of me..
which means the same as 8vb...off course..
btw: there is another challenge in this piece as i see it now...the last page of it he writes in 4/4 bar, 2 half notes on left hand and 5 quarter notes on right or 7 quarters on right..which is Ok...but left hand plays low e and octave higher f sharp or g chord on this half notes...which is impossible for small hands..(i cant take the e and g only f sharp i can take if my pink is on e) so in this case i take the g with right hand..which makes it very complicated because i have 5 or 7 quarters against 2 half notes as a said...so its unnecessarily difficult