Lets try it like this:
Risk $2,000 on parlays, 1k each way
1000= 2644 X 2 bets
......................................................................................................
you lose 2k or win 1644
assume no pushable lines
at the half, one loser, and a live ticket
now you can do one of a few things:
stand pat
or perhaps:
bet the 644 on the other side, if the middle is 3 points or better ?
644= 585
If you lose the 644 bet, you win the parlay, and break even.
You could win the H2 bet and the parlay for +2229
You could not lose all 3 bets
If parlays lose, -2000 +585= -1415
The H2 bet is the weak point, as it is blind and has vig.
Best is probably no H2 bet.
I'd play both parlays, but more on the one I liked better.