I think Sam has the makings of a good goalkeeper. He could take notice of a few Foster videos and notice that Foster was always on his toes when the opposition were attacking so he was well prepared for an unexpected shot and could move quickly in either direction.
He also stood in and around 3m off his goaline, which meant he had cut down the angle of the incoming shot by about 20%,allowing him to divert any inbound shot as he was on his toes and anticipating what was going to happen...he got this from years of experience and good solid concentration.
Sam does not have that concentration and anticipation ,yet. This will come in time. He is too flatfooted in preparation and clings to the goaline, hence when a shot comes in he cannot react as quickly or cover as much of his goal. This is why he seems flatfooted and fails to dive to keep out the goals he has conceded this year and last.
Foster rarely failed to attempt to stop shots no matter if he had no chance. He also had a great awareness on what was happening in front of him and was always belting out orders to his defence.
The goalkeeping coaches at Albion should be picking up on this.
I have coached keepers in the past and played myself ....I am not an expert,but can see these flaws in his game.