hybrid FH probably refers to a “mixed” usage of SFH and BBH, depending on the numbner of trx in the cell:
if the cell has 3 TRX or less – SFH is used with a MA list of 4 freq.
if the cell has 4 TRX or more – BBH is used
indeed, with a hopping list containing less than 4 freq., the freq diversity is not optimal. But above 4 freq in the list, there is not much more gain. The ideal value is 4.