Why do the front wheel arch plastic liners have a great big hole in them at the rear?

From what I can see, it will allow rain and muck etc front of the bulkhead into the engine bay?
Are they cut out for a reason? I have searched for after market MODS but none available.
Anybody here fixed this glaring ommision to the design at all?

Thanks

Twenty years ago I bought three year old 90 and the first mod it had was to fix some flexible rubber over that gap just trapping the rubber between the inner wing and bulkhead using the screws that join them and the lowest wheel arch fixing,outriggers and footwells still good despite all the crud a farm landy meets in that time Did the same for rear xmember and its still original.spray of oil once a year also helps, just dont park on someones posh drive for a couple of days.cheers

Good advice. Will look for some rubber to do this. Thanks