  Lattice scales defined using gradient flow are typically very precise, while
also easy to calculate. However, different definitions of flows and operators
can differ significantly, suggesting possible systematical effects. Using a
subset of RBC-UKQCD's 2+1 flavor domain wall fermion and Iwasaki gauge action
ensembles, we explore differences between $\sqrt{t_0}$ and $w_0$ gradient flow
scales, compare the impact of different operators to define the energy density,
and study the effect of using tree-level improvement for the gradient flow. We
find that for this set of gauge field ensembles Zeuthen flow with Symanzik
operators has the most consistent approach to the continuum limit and exhibit
very small cutoff corrections. Tree-level improvement, traditionally used in
step-scaling studies, significantly reduces the spread between different
operators, but does not lead to an overall improvement when it comes to
reducing cutoff effects for gradient flow scales $\sqrt{t_0}$ or $w_0$.
