I think the network IP address used to access the SW website also influences this combined with the cookies. Whenever I do any price checking during a SW sale, I always do this via an Incognito session so that I don't get a bunch of automated follow up emails to complete the booking as both SoCal and the Bay Area have many airport options that I check prices.
At my work address which is very close to ONT, the sales promos always default to LAX even during an Incognito session. At my home address, sales default to SNA, even though ONT is still the best convenience airport for this area with SAN as the closest "big city" airport which usually has the better deals. As doing a location check on any given IP address can return very broad locations that can be far away from the actual street address, I think this is a factor.
Both ONT and SNA are tough ones to find good low local sale pricing but every now and then, I get lucky and lock one in.
