I wouldn't book row 4 - not because of the curtain but because that implies a currently small CE cabin with the prospect of growing. If it were to grow you could find yourself moved to 25B or similar at the last minute, by which time better options may have been taken. You're probably safe from row 7 or so backwards if the cabin is only 3 rows at present. I tend to try for one of the exit rows if I'm in ET though.