Low as you can get safely friend. There is a chance there will be no wind so it will make no sense to fly lower than you want/need. But if you Battle head in wind , flying lower make a huge difference.
If you fly lower you will conquer lighter wind so you end up saving energy. Also be gentle on the sticks , to conserve energy too (spark will not brake and accelerate rapidly)
I have similar case but with the portable charging hub. The strange thing is when I put them( batteries) into the spark and just turn it on for a few seconds and the percentage will drop by about 1 and place my spark again in the charging hub it will start to charge them and then they will be...
Seems like the focal length of the lenses is off.
Maybe you took apart the gimbal or camera for cleaning and when you put it together you mismatch the lenses.
The focus point on the spark is set to infinity your seems to have now macro Focus point.
It's strange, because the fan is in enclosure and one hole is for intake and the second is for exhaust ,it is an forced Flow that runs through the cooling fins. Hope it still works.