Its extremely common to think a plane is closer than it actually is.

I don't know why, unless it's because there is nothing else in your line of sight and that makes you believe its closer as you concentrate on it.

It especially becomes a problem if you change to a bigger aircraft.

I like the suggestion of placing the plane on the landing strip and walking to where you will be standing when you are landing and trying to remember its size, which is all you have to go on to judge distance.

As with other things related to landing, practice helps.

-David C.