Not sure on #1, but I doubt it has anything to do with the strength of the signal being sent by the transducer.
For #2, do you have the latest updates on your unit? On my 997, one of the most recent updates gave me a 3rd menu selection when hitting the power button while the unit is on. The added option was to turn the sonar off, leaving only the GPS and it's associated screens working.
08 Skeeter SL210, F225 Yamaha four stroke, 798CI SI NVB, 997C SI
(formerly owned an 1197C SI NVB Combo)