But there's less head hits in this game...
Less head-hits as a percentage of total hits.
But consider the OpFor composition and the pilots. We frequently face OpFors that outnumber us 2-1 or 3-1, which results in a very high volume of fire. And pilots (particularly those with a few levels of gunnery under their belts) are substantially more accurate than in TT. The end result is a higher volume of fire, that is more likely to hit, than what one would find when playing TT.
To use a sports analogy, TT is a hockey goalie with a .870 Sv% (saves made/shots faced) and 2.30 GAA (the average number of goals scored against them over 60 minutes), whereas HBSBT is a goalie with a .950 Sv% and 3.50 GAA.
[EDIT] In case my analogy isn't clear: HBSBT has more head-hits than TT because HBSBT faces a higher volume of more accurate fire, even though head-hits have a lower chance of occurring on a per-shot basis.
TT goalie lets in fewer goals per game (has fewer head-hits), but has a lower Sv% (head-hits are more likely to occur on a per-shot basis).
HBSBT goalie lets in more goals per game (has more head-hits), but has a higher Sv% (head-hits are less likely to occur on a per-shot basis).