Wireless access points get placed for convenience more often than for coverage: wherever there was already a cable, or wherever the ceiling tile came out easily. That is why so many buildings have plenty of access points and poor wireless.
Coverage is about overlap, not count
Adding access points to a building with a coverage problem often makes it worse. Too many radios close together interfere with each other, and devices cling to a distant access point they can still hear rather than moving to the near one.
What you want is deliberate, modest overlap, so a device walking through the building has somewhere better to move to at each point, and enough separation that the radios are not shouting over one another.
What actually blocks the signal
Not distance so much as material. Plasterboard is close to transparent. Brick and concrete are not. Metal is a wall as far as wireless is concerned, which includes shelving, plant, and the racking in a warehouse. Water is a strong absorber, which includes stock and people.
This is why a survey done in an empty building overstates the coverage of a building in use. A busy room behaves differently from the same room at seven in the morning.
Height and orientation
Ceiling-mounted at normal ceiling height is right for most spaces, because the antenna pattern is designed to radiate downward and outward. Mounting an access point on a very high warehouse ceiling puts most of that pattern in empty air. Above a certain height, either a directional antenna or a lower mounting position does more than another unit would.
Where this meets the camera system
Access points and cameras compete for the same things: ceiling positions, cable pathways, and switch ports with power. Designing them separately means two sets of runs, two visits, and a switch that turns out to be undersized once both are on it.
Doing them together is cheaper and produces a better result in both, which is the whole argument for treating the building as one system rather than four purchases.
What a survey should actually give you
A wireless survey is worth having, but only if it produces something you can hold an installer to. A coverage map with proposed positions, the assumptions behind them, and a note of where the signal is expected to be weak is useful. A single page saying coverage is good is not.
Ask whether the survey was done with the building in its normal state. Stock on the racking, doors in their usual positions, and people present all change the result, and a survey taken in an empty unit will overstate what you get on a Tuesday afternoon.
Ask too what happens after installation. A verification pass once the access points are in is the step that catches the difference between the prediction and the building, and it is the step most often skipped because the equipment is already up and working well enough in the office.
Access points, cameras and the switches that feed them get designed together at Elite Security, because doing them separately is how buildings end up with two sets of cable and one undersized switch. More in the blog, or start with low-voltage cabling.