Hi John,
The spot position is fine for peaking but do expect the drive requirement to change once loaded up. The major caution is not to tune up in AM mode just in case you have the audio turned up with the final not yet loaded. This could cause something to flash over which is never a good thing
A little touch up to the plate tune or drive level is fine in AM but it is best to do any major tune-up (as when changing bands) in the CW mode.