That's actually a good idea; you'd probably get fairly reasonable results that way. The downside: using those tags at all makes it unambiguously clear that you care about the tip4commit tips.

One plausible possibility that might help: in the block that normally contains Signed-off-by and Reviewed-by, add a tag for marking a commit as "minor" or "trivial", in the sense used by the Linux kernel's trivial@ patches or the GNU project's threshold for changes accepted without copyright assignment.

And as a quick hack, scale the tip by log(diffstat) with a sensible upper bound.