1492 is the default frame size set by unifi on wan pppoe. You neither need to know such esoteric details nor need to set them.
“It just works”
You can also modify your frame size: Unifi Devices - Gateway - Settings - MSS Clamping.
In my view , unifi gives you all the power and very good defaults at a very reasonable price.
Their nearest competitors (eero on consumer side and ruckus / Aruba on business side) have less features and more price.
That behavior has changed a lot in the past decade. Apple actually documents their roaming thresholds.
The signal has to drop below -70dbm for ios and -75 dbm for macos for the devices to consider roaming. Additionally, the difference between the two AP has to be 8db for ios and 12 db for macos.
IMHO, these are good defaults. Apple devices are optimizing for stability over the “best” possible signal.
What you might consider awful signal difference between the two APs might not be. (e.g. a mac device at -75dbm need to find another AP with -63dbm or better.)
You can also modify your frame size: Unifi Devices - Gateway - Settings - MSS Clamping.
In my view , unifi gives you all the power and very good defaults at a very reasonable price. Their nearest competitors (eero on consumer side and ruckus / Aruba on business side) have less features and more price.