I dont think that adjacent interference influence the SDCCH drops.
to trigger the HO cell level should be (about) 5-6dbm for a while.
adjacent frequency should be better by 15dbm to influence its adjacent frequency. Hence, they can not affect each other. I mean if one of them is better by 5dbm than other HO occurs.
However, if this frequencies are not defined as a neighbor then they will affect each other.
If my idea is wrong please notice me.