The Gemara at the top of Daf 8b, questions what it means when the Braisa says 'placing an eruv in a pit above 10 tefachim, his eruv is an eruv'. The Gemara questions what is the case of the Braisa? If the pit is 10 tefachim deep, and 'Lemayla' means he was 'Dali V'osivei', lifted it and rested it above higher than 10 tefachim from the floor.
Why does the Gemara suggest 'lifting' the eruv, as if first it was in a lower position?. Why not just say 'Lemayla' means he placed it higher than 10 tefachim from the floor?
Ramat Beit Shemesh, Israel, Ramat Beit Shemesh, Israel
I think that when the Gemara says "de'Dala'i ve'Osvei" and "de'Tasa'i ve'Osvei"',
it means 'he placed it high up' and 'he placed it low down' respectively, just as you suggested. It does not mean that he first put it lower and then raised it.
b'Virchas Kol Tuv,
Eliezer Chrysler