Curve size how do you mask them

You could try spiraling down each section of track from larger to smaller radii. That is what the real RRs do.

Some folks hide turnarounds between buildings.

Easements.

So lets talk easements, if one has a hard limit of 042 for a return loop if you enter the curve with a gentle curve what would the apex of the curve be, less than 042, more, something i am not considering?

With an easement the diameter/radius of the curve remains the same--what is changed is the transition from the straight track into the curve. There are many techniques to lay out easements. One approach with sectional track is to use several different diameters leading into the main curve--not optimal but easy to implement.

Obviously you'll need a bit more real estate for the curve but the will be better both visually and operationally--"easing" into the curve.

Easements will not hide an 042 curve.

There are four 031 & 042 return loops on my 3 rail layout either hidden in mountains or off scene.

0120" and 0148" curves are visible on the mainline between the mountains.

Eye level at a distance the Rail King trains are not that non scale in appearance.  In fact because the rest of the layout's track is all two rail at viewing angles it influences a visitors perception.  No one notices the GG track at first.

If you have a desire for broad curve consider going around the room with shelf benchwork.

Any island platform will constrict any curves.

True spiral easements developed with a flex track transition will only add +/-2" of width to a 180 degree curve.

A sharp curve often looks less so when viewed from the inside rather than the outside.