Standing Layup for sure affects simulation stats but I don't think Shot Under Basket does anything. I don't see a difference in game or while simulating when I tweaked it.
Look at the hot zones in the player edit section. The Close Middle/Right/Left is what the shot close tendency covers. The player may still shoot from there even if the tendency is at 0 depending on other factors.
I feel like it's a modifier for the overall shot tendency. The higher it is, the more aggressive a player will be in looking for their shot, particularly around the hoop.