Water leaking through front door and inside threshold bar

[homeprw]

During heavy rain there is a small amount of water seeping through the seals on the inside of the front door frame. Water enters here and into the channel in the threshold. I intend to replace the seal but it's my understanding that water can and often does seep through the seals at the front door where it can collect in the threshold channel which for this purpose has drainage holes at the front. Water then exits through these drainage holes back out to the exterior. However, in this case this doesn't seem to be happening as there are two further holes at the back of the threshold channel which I don't know the purpose off but appears to be the source of the leak as water is making it's way to the interior. The front drainage holes are clear and unblocked. I did a test by pouring some water into the threshold chanel to mimic the water ingress and no water exited to the exterior through the front drainage holes but instead drained away through the back drainage holes in the threshold channel as for some reason these holes are slightly lower than the front holes. I've no idea where this water then drains too but can only assume below the threshold and therefore into the interior so it's strange to me that these holes actually exist in the threshold channel. Does anyone know the purpose of these holes?

I've attached an image showing a plastic tie pushed through the front drainage hole of the threshold (marked1) which then passes through the channel and into the other hole (marked2) at the back of the threshold. This is where water disappears down when it enters into the threshold channel, this hole being slightly lower in the channel compared to the front drainage hole.