how to max delve exp past mlvl 83?

hi, I sort of like delve but have been noticing that at mlvl 83
the xp you get barely goes up as you go down. packsize and increased
magic / rare mobs as well as vaal cities etc are about all I can
see improving the xp income.

is there any reason to keep going straight down xp wise? or should
I be branching off sideways looking for packsize / magic/rare and
vaal outposts/cities etc. ? also does going straight down result in
worthy rewards? (obviously more quality/quantity of fossils)