According to R Yosef and Abaye if the bed is 10 tfochim high can you say shma, rashi seems to hold that it is not covered i.e. it is ossur. so what is the svoro of reshus acheres? Does it mean that the bed is so high to be a different reshus so it can't be said to cover? on the other hand if it a different reshus then the keili is as if it is in a different room, if we say gud achis mechitzos, so why is it ossur?
Moshe, Gibraltar
1) Rashi writes that if the bed is 10-Tefachim high, it looks as though the Mei Raglayim are not underneath the bed, since there is such a big gap, so the bed is not a cover. It seems, as you write, Moshe, that according to this, "Reshus Acheres" means that the bed is so high that it cannot be considered as covering the urine. The Mei Raglayim is not considered as being in a different room. It is in the same room, but it is as if the bed is not there, so the bed cannot help to cover the Mei Raglayim.
2) Talmidei Rabeinu Yonah writes that "Reshus Acheres" means that since the bed is 10-Tefachim high, it follows that what is above the bed has become an independent Reshus, and what is below the bed is also an independent Reshus, so the higher Reshus can no longer cover over what is in the lower Reshus.
3) I am not aware that we ever say "Gud Achis Mechitzos" for a bed. Even for a Sukah, where we have proper walls, the opinion of the Chachamim in the Mishnah in Sukah 16a is that if the walls are more than three Tefachim away from the ground, the Sukah is invalid.
Kol Tuv,
Dovid Bloom