NBA Spreads of 10+ and Totals of 200+, Are Unders More Likely

A former coworker suggested this hypothesis: when looking at large NBA spreads (say where a team is favored by 10+), coupled with a large total (like 200+), are unders more likely? The reasoning being that the heavy favorite is likely to run away with the game (regardless of whether they cover or not) and then coast for a large part of the game, leading to lower scoring.

I looked at the past 5 seasons of NBA spreads and totals, and first I just checked ATS of 10+ and O/U of 200+. This occurred 7.38% of the time, and returned an "under" percentage of 51.61%, which isn't enough to hurdle the juice at -110 (52.38% is needed).

Next I ran a non-linear optimization algorithm to maximize the percentage of unders, while changing the spread and totals variables. And there is a combo threshold that results in fairly optimal unders cashing: spreads of 9+ and totals of 210+ saw the under hit 54.73% of the time. This situation occurs much less frequently, only showing up 3.18% of the time.

NBA Unders	% Occur	Win %	Return	ROI
ATS 10+, O/U 200+	7.38%	51.61%	-7	-1.43%
ATS 9+, O/U 210+	3.18%	54.73%	9	4.53%