I actually think lost souls should be removed from high reaper. Incidence should taper down from max at r1 to none in r10.
I was quite surprised when I came back to the game and reaper had been introduced, a mode meant to be unfair and that was trying to kill you, to find lost souls were ubiquitous in high skulls. Part of the challenge of a caster, in times past, was mana conservation. So a more challenging game mode obviating one dimension of challenge seemed strange to me.
It's fun to get spent occasionally. Then you have to make decisions. Do I use some resources? Do we try to play carefully until the next shrine? Do we make a detour somewhere? And when you reach a shrine, gasping for mana: the relief! This aspect of the game seems hardly to be found now at cap.