If you look on page 23 of the installation manual, one of the troubleshooting questions is, the whip is too long or too short. The answer is to extend the conduit with a warning to follow electrical codes. That suggests you could mount it further away but man what a pain.
I don't follow your geography, but if it is in the corner, you might mount it on the wall adjoining, with the conduit cutting the corner. That's how mine was installed, because you can't mount it below the panel. You might be able to mount it above the panel.
SecretSquirrel - can you verify this is OK? I think as close as possible is OK - few feet should be acceptable but I'll defer to SecretSquirrel for confirmation.
The Site Preparation and Installation Guide for the UTS6H Transfer Switch states "install the UTS within one foot of the building circuit breaker panel." Is it critical that the UTS be located within 1' of the breaker panel? The breaker panel for my house is in the corner of my garage, sandwiched between a wall corner and the garage door frame. The wall studs prevent me from installing anything else within a couple feet of the breaker panel. Is it OK to install the UTS more than a few feet from the breaker panel?
My "scientific guess" would be that the instruction to install the UTS within one foot is based on the length of the "whip" attached to the unit for connecting to the circuit breaker panel. Moving the UTS any further away will require replacement of the provided flexible conduit and connecting wiring within the conduit. Not impossible, but sure will add to the installation effort! I'll rephrase what Angela has already said with "closest possible is best".
I too am interested to see if or what APC recommends for a maximum distance from the circuit breaker panel!
How far from the breaker panel do you think you need to go?
Choose a location