1. A method in a receiving node for assisting a sending node in performing adaptations of a rank for transmissions being received by the receiving node over a multiple-input-multiple-output (MIMO) channel, the rank being one out of a set of different ranks, the set of different ranks comprising a first rank and at least one second rank, the method comprising: performing measurements on one or more reference signals received from the sending node; performing a first feedback computation for the first rank, based on the performed measurements, by applying a first relation between assumed transmitted energy for data and transmitted energy for the one or more reference signals, wherein the first relation is specific to the first rank and wherein a second relation between assumed transmitted energy for data and transmitted energy for the one or more reference signals is specific to the at least one second rank; performing at least one second feedback computation for the at least one second rank based on the performed measurements; selecting a rank out of the first rank and the at least one second rank based on the performed first and at least one second feedback computations; and indicating the selected rank in a feedback report to the sending node.