What is your approach to post-kidney transplant erythrocytosis for an asymptomatic patient already on ACEi but with Hb consistently >18?

My approach is to rule out non-transplant-associated causes of erythrocytosis (examples include obstructive sleep apnea, checking for renal artery stenosis, etc.). Once the diagnosis of post-kidney transplant erythrocytosis has been met, we typically use ACEi/ARB as you mention in the question. If that does not improve the hemoglobin, we can institute therapeutic phlebotomy. The thresholds for when to start therapeutic phlebotomy vary, but I tend to target a hemoglobin less than 19 g/dL.