G-EMMA, in reply to your questions about Ground Effect, there is a rather "techie" treatise to be found
here.
From this article, it would seem that about 70% of the span-dominated ground effect is lost at a height equivalent to 20% of the aircraft wingspan and it becomes negligible at a height of 100% of the wingspan.
The wingspan of a PA28-140 is 30 feet, so 20% represents 6 feet. As the wing is already 3 feet agl when the wheels are on the ground, this means 70% of any benefit would be lost when the wheels are 3 feet above the ground and there is virtually no beneficial effect at 27 feet agl.
The chord-dominated effect seem much more complicated, so I'll leave you to read the rest ...
Hope this helps.
JD
