As an Engineer for a Wireless manufacture, I get a lot of questions about wireless design. For those of you who have done this, you know there is more than one answer to every question. The question of why is it so hard is best explained with a story and a picture. Down the road from my house is a new hotel being built. Hotels are nightmares for wireless with all the rooms and long hallways, multiple floors, gadgets to interfere, etc. Most interior walls are Sheetrock and the floors are pretty thick, so this should not be that bad. Do a heat map and you are good, right? The heat map is done and still you have issues. Why? Maybe this hidden gem will help.
All the wall are filled with steel studs. This is a reflection nightmare and it is all hidden behind the Sheetrock. Unless you saw it getting built, you would never know the studs were steel. This is why it is hard. RF energy has so many rules if you know all the variables. News Flash!!! You will never know all the variables. Moral of the story is you plan, design, pray, and hope for the best. Under sell and over deliver. Always do heat maps with worst case scenarios and the real world will never be that bad. No heat map will replace an onsite RF Survey, but it is a start. Just my thoughts when I saw the above picture.