Nami - W - Ally Heal only ~half what tooltip states - yet - full heal on self

Playing two ARAMs tonight as Nami, I noticed that any heals from my W on Allies was only a MAX of ~148-186 when the tooltip itself reports at lvl 18 " the torrent heals the target and bounces towards a nearby enemy champion" for 185 + 50% AP scaling. Now in each of these ARAMs I easily had 400+ AP, so at 50% scaling + the default heal, should have been healing at the first hop at least 385-500 life.
This however seems to have been mitgated by the players current magic resist. Any allies without MR, were receiving full heals (including myself).

Is this a new bug? It was not like this the last few times I played Nami, which was admittedly at least 1-2 patches ago.