Too big tin for meringue cake recipe. How to solve?
Both solutions will work.

If you are making more mering, then make sure the thickness of the meringue layer in stays the same as for the small tin. If you scale the recipe correctly this happens automatically.

I think your math is off though. The area of your 24 inch tin is only 1.77 times larger than the 18 inch pan. 

Assuming your pan is round: The area of the large pan is pi*24^2 and the area of the small is pi*18^2 the ratio is therefore pi*24^2 / pi*18^2 = 24^2 / 18^2 = (24/18)^2 = 1.77 .

If your pan is square the (almost) same computation will give the same result.