Your best chance of improving the range is at the receiver and whilst there find out if it is an Elsema or ATA, there may even be both brands in use and these handsets although using the same operational frequency are slightly different and so are the receiver boards.
Your dip switch code settings appear to be the same but on some earlier units the settings would be inverted on one of them when used on a single receiver, the reason for this is simply that they are or were two independent manufacturers so cross compatibility was never a consideration.
You also need to be careful as other residents will have remote access so dont touch the receiver settings or trim pots, you may be able to just add a small whip antenna to it, 10 to 25 meters is acceptable for these so I wouldn't be to worried about it unless you are regularly approaching the driveway entrance at 100 kph, you can get up to and beyond 100 meters on the Elsema's if you know what you are doing.
Muttley