laying of pex and controls

Gary Usa_2

would someone be kind to help me with the following,i have seem many different ways that pex is laid down and installed,here goes another silly question ,when pex is laid down i have noticed that on a return that pex is laid with a bell shape on the return,is this so that you can get the spacings better and not putting the pex under such a strain ,doing it this way wouldn;t it give the floor and uneven heat,now what about if you laid pex down in a circle formation wherethe pex could then be evenly spaced apart and uniformally giving a good even heat.

is it always good practice to say leave a 6 inch space between the wall ,to the the pex.

with relation to controls why arnt 4 way mixing valves used more,or is it due to cost etc.

thanks guys as always hope that you are all keeping well

all the best

gary usa