What hardware factors affect range distance of consumer grade router?

If you mean, "feature X provides Y amount of range", there's not really a particular hard & fast rule. Sure, the engineers building these things will know what features produce a particular signal strength under ideal/testing conditions...but a lot of that goes out the window once they're "in the wild".

Essentially, though, here are some things to consider:
-- External antennae usually provide a stronger signal than internal antennae. Mainly this is a size issue, though: smaller routers don't have the room for big internal antennae, so they can use larger antennae to broadcast a stronger signal. This is an area where you can boost the signal further by removing the antennae & replacing them with larger/stronger ones. This is also why some people buy wi-fi boosters/repeaters, especially in very large homes.
-- More antennae = stronger signal. Basically, assuming antennae of the same type, the router with 3 antennae should have a stronger signal than the one with only 2. If you have the option, get the router with more antennae (3 is better than 4, 4 is better than 3, etc.).
-- Channel selection. Having worked in tech support before, I can tell you straight out that most people never change the default settings for their wireless router... & even if they remember to change the default SSID/key, they never change the channel being used. Since 99% of the routers use channels 1, 6 or 11, that can leave you open to interference from your neighbors' routers. If you can see a lot of available networks when looking for the one to connect to, try manually selecting a different channel in the router. Note that this may not have as much effect for Wireless-N routers.
-- Location, location, location. Sticking a router in the back corner of the basement & expecting to get full signal strength in the 3rd-floor bedroom is a recipe for disappointment. You can sometimes get a "dead zone" by getting too close to the router -- but let's face it, if your PC is going to be less than 10ft from the router (especially if it's not going to be moved around), you should just be springing for the CAT5/6 cable anyway. In any case, having more than a floor (or maybe 3 rooms) space between you & the router means you may start having signal issues. But even then, you may still have a decent connection -- I can get 2 out of 3 bars on my iPod touch when I'm standing 20 feet from the back of the house (which is about 40-50 feet from the router itself). Ideally, try to place your router as centrally as possible, so that you only have issues in the outlying areas; my router is in the "computer room", & is actually almost dead center in the house, so all of the rooms have great reception.
-- Housing materials & other environmental factors. Wireless signals are literally radio signals (i.e. when radio was first invented, they called the transceivers "wireless")... so anything that interferes with a radio or TV signal can affect the wireless router signal as well. For example, my house was built in the 1950s, & they were built with metal reinforcements inside the walls (not a true "steel house", but pretty close), which means that cellphone & TV reception is sometimes spotty. Also, having other devices that use a close frequency can cause issues (i.e. 2.4 GHz cordless phones can interfere with Wireless-G routers). If you get issues with signal strength changing radically when you move around a single room, there're probably some environmental factors involved.

You have to be very very careful about terminology.

802.11n does not have 2 times the range. It has exactly the same range because the transmit power is regulated. It does not matter what you transmit. It could be 802.11ac or a baby monitor you can only put out a fixed amount of signal.

The reason people get confused is because they are factoring in the amount of data. A sorta fake example to avoid lots of details.
Lets say a signal level x you get 50m/sec on 802.11g and 100m/sec on 802.11n (because N is more efficient at putting data in)
Then say a signal level y you get 25m/sec on 802.11g and 50m/sec on 802.11n

If your requirement was I must have 50m then 802.11n has more "range" but you still actually have signal from 802.11g it just is deemed not good enough.

The problem with this method of determining range is when you get to the edge of the actual signal coverage it degrades rapidly so it really doesn't matter what encode you are using pretty much a encoding system that passes 2 times the data is still passing 2 times nothing.

Bottom line on this is if you have no signal the encoding method used will make no difference.

Antenna size to a point makes a difference but if you go too large all you manage to do is violate the laws. The radio and antenna are fairly closely matched and you can only go so far before it actually starts to degrade the radios ability to transmit. Reception though is a different story generally larger is almost always better. The key here is the router is only half the equation the equipment on the other end also needs to be able to transmit and receive the signal and its radio and antenna play a role.

Number of antenna if I ignore the beam forming in 802.11ac does not increase the range either. Again this is the definitions of "range" that includes data rates. When you use multiple antenna system they use something called mimo that transmits multiple overlapping signals and user the antenna to separate out the signals. So at a given signal level I get more data but it does not increase the signal level itself