I’m sure ET will chime in with a fuller explanation but in the meantime:
HeadSpace had four heads and they all add to the overall volume of the output. I experimented with little to no delay time (I was specifically exploring the rec drive feature) and had the same trouble as you. To solve my problem I turned the individual head levels down and/or used fewer heads. I expect this is less of a problem with longer delay times.
Also note that the point of maximum volume on the MIX control of most H9 algos is about 2 o’clock (50). Based on experimentation, I believe that is also true of HeadSpace (about 7 on the HS MIX control).