Skeletons in minecart and with followrange extended do not see you, when you are also in a minecart riding, with 1-25 blocks distance from the mob. And they are shooting not accurate.

Reproduce, let a skeleton spawn on poweredtrack. and you also, use detectorrail and a commandblock to spawm the skeleton. the skeleton is minecart will ride behind you and should trying to shoot you. but no, he does not see you. and is sometimes shooting very unaccurate.

/summon Skeleton 1856 63 -263 {Equipment:[{id:bow,Count:1,tag:{ench:[{id:48,lvl:2}]}},{},{},{},{}],DropChances:[0.0F,0.085F,0.085F,0.085F,0.085F],Attributes:[{Name:generic.followRange,Base:30}],Riding:{id:"MinecartRideable"}}