When building a set of zoomies and customer wants EGT. I like bottom and about 4" out if possible. The furthure out you move them the lower the temp will be at any point,in other words. If you normally have 1050 target temps and you move EGT 2" you will probably be burning pistons around 1000*,just example. If you have data from another setup put them as close to same distance as possible,if not then its where you like them. As for bottom I have been told some data recorder company's want them on top.IMO if you have probe center of pipe it should not matter.